Sentinel is an interactive audio tower defense game. It mixes strategic gameplay with a dynamic music system.
User reviews: Mixed (45 reviews)
Release Date: Apr 22, 2014
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Recommended By Curators

"Fantastic soundtrack wrapped in a visualizing and challenging tower defense coat that is incredibly challenging and more of a puzzle than usual TD fare."
Read the full review here.


“If you’re quite fond of the tower defense genre, then you’d certainly be wise to add Sentinel to your play list.”

About This Game

Sentinel is an interactive audio tower defense game. It mixes strategic game play with a dynamic music system.

The game takes place on a sequencer-like grid. As you add defenses, collect resources and destroy enemies, musical elements are triggered in time to the music.

Fight through 31 levels to clear the virus from the system.

System Requirements

Mac OS X
SteamOS + Linux
    • OS: Windows XP or later
    • Processor: 2.0Ghz+
    • Memory: 2 GB RAM
    • Graphics: Shader Model 2.0+
    • Hard Drive: 750 MB available space
    • Additional Notes: Widescreen monitor required.
    • OS: OSX 10.5 or later
    • Processor: 2.0Ghz+
    • Memory: 2 GB RAM
    • Graphics: Shader Model 2.0+
    • Hard Drive: 750 MB available space
    • Additional Notes: Widescreen monitor required.
    • OS: Ubuntu 10.04 or later
    • Processor: 2.0Ghz+
    • Memory: 2 GB RAM
    • Graphics: Shader Model 2.0+
    • Hard Drive: 750 MB available space
    • Additional Notes: Widescreen monitor required.
Helpful customer reviews
8 of 10 people (80%) found this review helpful
1 person found this review funny
0.9 hrs on record
Posted: March 16
The emphasis on needing to get “perfect” levels killed the game when I reached the first gate. I cannot do it on any level. There is no “easy” mode or anything. You just have to get an absolutely perfect level to progress. Apparently this idea multiplies throughout the game for the rest of the checkpoints.

Mr. Brown, why not just have a simple progression system and just give an achievement for the perfectionists? The whole game is locked down basically :/

Like others have said, lots of mirco-managing, flashing colors, etc, but I didn’t mind any of it – pretty fun game for me and the micro-manage craziness actually had appeal… for the first 5 levels… till I got stuck… by needing at least one to be perfect. ^_^

Because of the craziness of switching your power back and forth from tower to tower, collecting money that’s falling, and using the manual tower, lots of things are happening very quickly – so to expect everybody who plays the game to be able to do that perfectly is a bit.. lame.

I never go for “100%s” or “max levels” or “all gold times” in games, I just like progressing casually. This is not possible in this game, you must be perfect... while you pay attention to 10 things at the same time.
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4 of 4 people (100%) found this review helpful
4.8 hrs on record
Posted: April 27
tl;dr -> Never has a tower-defence (TD) game made me rage so much at trying to 100% each level. 11/10 get my electronic groove fix.

I got this game gifted to me by a generous friend, and was very excited to try it because of the music, artstyle, and effects. I was extremely pleased with my experience.

If you like tower-defence games, managing multiple tasks rapidly (this is very, very important), electronic music, and fancy effects, then you will really like this game.

The aesthetics are very nice - the colors and backgrounds are alive with vivid color. The music is one of the most important elements in this game, and the tracklist is composed of very good electronic music. I strongly suggest you take a look at the trailer provided to get a feel for the music, or even search for the soundtrack on YouTube - the genre may not be to your liking. That being said, I absolutely love electronic dance music (EDM) and most subgenres related to it, so be aware of my personal bias in this regard. Note, the tracklist is more groovy, chillout electronic than the intense type typically played in clubs and on the radio - so don't expect buildups and drops.

I found the music to be wonderfully fit for creating a fun atmosphere despite that many times contrasts with how much task-switching you have to do during gameplay. As the beat progresses, a light flashes left-to-right across the level/background. If you have activated turrets, they will flash when the light passes over it, and the more turrets you have activated, the deeper/fuller/louder the music sounds. You will notice that the music will dull down whenever you have no powered turrets. The dynamic music (interacting with your turret placement) is done very well and has no effect on gameplay besides aesthetics.

The controls are simple - everything is done with the mouse - however, managing your actions/tasks is the most difficult part of the game. There is a very quick and helpful tutorial that begins right you start a new game, and the opening sequence is great. The learning curve is minimal to moderate depending on your familiarity with tower-defence games, but be warned - the game involves a lot of task-switching, so quick reflexes are essential if you want to avoid getting overwhelmed.

Gameplay involves you defending your core against waves of enemy viruses coming from different paths (numbered 1-x). There is a tracker that shows you what creeps are incoming, however, there is no real way of knowing what each virus does until you encounter them (no tooltips, no virus encyclopaedia, etc) and see for yourself. There are a variety of towers to use, each with different strengths. For example, there is a quick-firing beam that removes enemy shields, a slowing program, and an anti-worm (these are yellow non-circular viruses) program. Whenever you place a program there is a cooldown timer before you can place that specific program again. To counter this, a (quite expensive) cooldown reset ability can be purchased (refreshes all towers; must be bought each time you want to use it). There is also a free "manual aim" tower that can be placed, and I strongly suggest you place these whenever they are available to maximize your combat potential. To use the "manual aim" programs, you must click on them, then click and hold anywhere within their attack area. After a certain number of attacks (indicated by a bar underneath the tower), the program will disappear.

As you play, resource pickups will periodically drop from the top of the screen to a random part of the level - you need to click these to obtain the resources. Enemies will also sometimes drop smaller pickups, which are used to either upgrade your programs (up to a level of 2) or buy special items from your core. For example, you can buy a mine for 1 upgrade point, which allows you to place one-shot proximity mines; for 2 upgrade points, you can unlock a power generator program that supplies you with one power.

You start each level with a set number of power points needed to activate your programs. Whenever you build a new program/tower, it comes powered with 1 bar. You can use the mouse wheel to divert power to and away from your programs, and this is something that gets crazy as you progress deeper into the game. For example, you may have one tower with max power near the beginning of an enemy path, but once the creeps all make it past your program, you quickly cycle all the power out of that tower and divert it to your other programs further down the pathway. You must make these decisions in real-time, and it can get chaotic when a large amount of enemies are bearing down on your core.

There are gated checkpoints in the game that require you to beat a certain number of levels before you can proceed further. There is an icon given to you whenever you complete a level, as well as a second icon for achieving 100% (no damage to your core). I love tower-defence games and play a lot of them, so I give you all a warning: this is one of the most infuriating games to try to 100% (not necessarily a bad thing). It just takes one creep making it past you to ruin your run. Worse so are the bonus levels.

Aside from the main levels are bonus levels - which are scenarios that require you to use certain strategies. For example, one bonus level that took me ages involves you using the "manual aim" towers to soften up waves of enemies so your towers can finish them off. The catch? You have to make sure you attack each enemy the correct amount because you are given no resources to build more towers. There is another bonus level that taught me how to take advantage of programs and power (sometimes it is better to just buy a cheap program to get the extra power point) - you start off only able to build power stations, and the only available spots are at the bottom of the screen. To beat this stage, you must build power stations at the bottom, cycle power off, and divert it to the programs already supplied to you.

Overall, the game is a great staple of the genre, and anyone interested in electronic music, TD games, and being challenged should definitely give this a try.

Highly recommend!

DJSF @DJSF's Rogue Reviews

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3 of 3 people (100%) found this review helpful
3.8 hrs on record
Posted: December 4, 2014
What a great surprise was to find this game in last Autumn Sale'14!

Tower defense genre, with a twist: the limited energy resource, that must be managed and relocated between the towers at all times.

Besides that, the futuristic theme is eye candy, and there is an awesome electronic music (of a style i do not know how to determine precisely if it is minimal, house...) soundtrack.

The game works like a kind of sound synthesizer, since each kind of tower makes a different sound.

I like the difficulty, and is specially rewarding when your solution is correct and the remixed music sounds good!
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2 of 2 people (100%) found this review helpful
3.1 hrs on record
Posted: February 10
I buy everything Matthew Brown puts out. Hasn't disappointed me yet. Nothing totally new about this game, but it does manage to turn what could be an annoying tower defense mechanic in other games into a much more entertaining puzzle than it rightly should be. The musical nuts and bolts holding this game together make it a must play. Be ready for a challenge.
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2 of 2 people (100%) found this review helpful
13.6 hrs on record
Posted: April 7
As far as Tower Defense games go, Sentinel is a work of art. It combines some of the best and simplistic elements and crafts them together to form one excellent and strategic game that is very fun to play in bursts.

Sentinel has the basic Tower Defense gameplay, defending against hordes of oncoming enemies (or "Viruses" in this case) each with different strengths and weaknesses. It's main feature that gives it it's individuality aside from it's futuristic digital theme is probably the power consumption mechanic. Without any units of power, your defenses can't function. For each defensive object ("Towers" or "Anti-Viruses" or whatever you want to call them) you have deployed on the grid, you are supplied with one additional unit of power on top of the amount you are provided with by default (this varies from level to level), each defense can use up to 5 units of power, 1 being the minimum amount required to be funcitonal, 2 units through to 5 units supplies the defense with a strength and / or range boost. It sounds a little bit complicated, but it's very easy to learn after a few minutes of play.
Managing power in Sentinel can be very difficult and requires a lot of micro-managing, particularly because more often than not you'll need to sacrifice one of your operational defenses in order to activate another one on the other side of the grid. This game actually requires you to think rather than blindly placing defenses all over the place, especially in the bonus levels, just another thing that makes Sentinel great.

One of the other things pushes the right buttons for me is the theme and art-style in Sentinel, as you can tell from the screenshots and trailer it has cyber and futuristic features which is already a selling point to me, but on top of that it also includes some rthym elements, meaning that the background music ties in well with the gameplay. Already a definite must-have for my collection.
It's simple and minimalistic menu interface and level selection themes are also really well made, the game is just very easy on the eyes and pleasant to look at.
The interface is very simple and user friendly, thus easy to understand and can be picked-up very quickly, things like the radar will be crucial to your efforts when you begin playing and have learned the strengths and weakneses of each enemy.

The game is however not without some flaws, it has a "Gate" system which requires you to complete levels to acquire credits (at least, that's what I call them) in order to pass through to the next stages, while I don't have a problem with this mechanic, it will likely feel grindy and tedious after a while as the basic level completion credits are not enough to pass through all of the gates, you have to acquire more credits by defeating those levels again without the core taking any damage at all from incoming enemies, much easier said than done on a number of levels. This isn't a problem for those of you that like a challenge, but it can slow down progressing through the game a fair bit as all it takes is one virus to slip through to the core to force you to restart the level once again.

So all in all, considering the fact that this is a game that I acquired in a cheap bundle, it's a bloody good one. If you're into Tower Defense or Strategy games, add this one to your collection, it's a very affordable and fun game to play for when you're in that "I have nothing to play" mood. Honestly, I just wish there were some more levels to play as for me it ended too soon.

Matthew Brown, please consider a Sentinel sequel or some DLC.
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1 of 2 people (50%) found this review helpful
0.1 hrs on record
Posted: December 14, 2014
Pretty cool tower defense game where you can actually controll the power that goes into every gun you place, affecting their range and power, and making use of a minute amount of energy; you can't max out all of your turrets and call it a day, you have to pay attention to where enemies are coming from and power them up accordingly.
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30 of 37 people (81%) found this review helpful
1.1 hrs on record
Posted: April 22, 2014
It's a simple, tower-defense game, nothing game-changing. But it's still fun, challenging, and forgiving at the same time.

Here's a quick look I did of the game. Feel free to skip around to get a general idea of the game and what you'll be getting into. Or you can simply read my summary below.

I'll start off by saying it's got a good atmosphere to go along with what it is. The basic premise is that you're an anti-virus program defending off viruses, and the visuals and music that accompany it fit their their roles well to put you into that world.

The basic gameplay is simple. You have lanes of creeps that mindlessly run into your core. The bare bones of all TD games. However, the game isn't as simple as plopping down a tower and forgetting about it. You have to allocate a limited pool of power to to each tower, and the more you give it, the stronger it is. So you're always frantically shifting your defenses around as the waves progress. That means you aren't staring at the screen and letting the game play itself, which is always a good thing. You also have to click little cubes and diamonds for ressources to upgrade and build your stuff, so you always have to be on the lookout for those. The game even grants you a free limited-time tower to help clean up some of the creeps that make it through, which is also nice. Nobody likes banging your head against the keyboard as the final creep runs into the core with only a sliver of health, ruining your perfect run.

The music is also good, if repetitive, but that's kind of what techno is all about. I also really enjoy the fact that the music changes as you add power to different towers, and that when the tower themselves fire, they also add to the beat. It's almost as if you're remixing the song yourself.

But now let's talk about some of the negatives. While the game does give you a good tutorial to get you started, it doesn't do a good job explaining the newer things you get later on down the line. It's all about trail and error. You also have no idea how much of a difference you're making when you upgrade a tower or give it power. You get a visual cue that the range has increased, but not about how much extra power you're giving it. A percentage or something would be nice to have. Also, the game kept on sending in new enemies at me that I had no idea how to deal with properly. The first being a big cube that only slows down when you constantly hit it with something. But the only thing that constantly fires is the free tower that's on a long cooldown. You also have to control it manually, so you can't allocate resources or build new things until you've finished dealing with the threat. Then the game snowballs into something you can't recover from, so you have to start over.

Then there's the problem of not knowing how effective a certain tower is against a certain enemy type. I got a tower that was supposed to be effective against shielded enemies, but when they came, even at full power it wasn't that great. And when you start throwing other normal minions into the mix, you're never sure what tower you should prioritze over another as they enemies bum-rush you from all directions. And not only that, it's extremely frustrating when the tower that's effective against certain types chooses to fire at another enemy, and the one it's supposed to kill struts by unscathed. There needs to be some sort of target priority.

But yeah, all of that is only a problem if you're OCD like me and want a perfect score. There's plenty of lives you can leak before you get a game over and have to retry.

So in summary, this is a solid TD game at $3. The game offers good content, a variety of enemy types, keeps you engaged constantly in what's going on, interesting setting and music (if you like techno), and is genreally just a good time waster. Get it now, or even wait for a sale when this game won't cost more than a dollar. You'll get some enjoyment out of it.
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9 of 9 people (100%) found this review helpful
2.7 hrs on record
Posted: November 11, 2014
I have mixed feelings about Sentinel...

As a TD game, you have to micromanage a lot of little things very quickly and keep checking the upcoming waves to know how to deal with each one properly, however, unlike most TD games, the strategy doesn't come from placement or upgrading, but rather energy. In Sentinel, you have a set amount of energy (and adding a tower to the field increases that amount by 1) which you can divide among your towers, to a max of 5 energy at any one tower. You can later reduce energy in one tower to give it to another, to focus your attack on a different lane. This is the main mechanic of the game and takes serious micromanagement skills. During each round, random extra money might fall from the top of the screen for you to collect, and dead enemies might drop special icons that allow you to upgrade or buy different towers, and while the game itself isn't terribly fast-paced, all of this happening at once makes for a real challenge keeping up with it all.

Outside of the TD, there's a stage-select map, which I actually quite like, apart from the gates you have to "hack". Every so often you'll come to a locked node that you can't get past without spending a certain number of "credits". Each stage gives you 1 credit for completion and 1 for getting through it perfectly (and bonus stages give just 1, since you have to do it perfectly or fail). As you get to the later gates, you realize very quickly that you'll have to go back to some levels and get a perfect on them if you want to continue. I find this a little frustrating, as in my (admittedly limited) experience with TD games, I've never had to do a round perfectly to move on to the next.

That's about all the bad I can think of for this game, though, and there's plenty of good to mention. First and foremost, it's just fun! The music suits the game very well, going from calm and relaxed to active and upbeat as you change stages, and it's always very unintrusive, letting you focus on the gameplay. Although it does take skill to use properly, I like the energy mechanic as an idea, being able to focus more on one part of the field at first, then spread out your power later, or turn off a useless tower that round to make a more needed tower a bit stronger.

The bonus stages really make you think about every little detail of the game, from which towers to place where, when to have them on or off, how much energy they need, when to sell them, when maxing out their strength isn't a good idea... the list goes on and on, and each one is very cleverly constructed to make you aware of some aspect you may not have known before, making it a very cool way to teach the player without sitting through a tutorial. One example that really jumps out at me is a bonus stage near the beginning, where you have to collect the early enemy drops to upgrade your towers, and then sell them because the upgraded ones are worth more, and that gives you the money to set enough mines to take out the remaining enemies which can't be destroyed by the towers. If you do it perfectly, you will end up with zero money, so there is no room for error, and you definitely have to know what you're doing to get the job done.

For me, $3 is absolutely a bargain. I'm getting a fresh twist on a cool genre, and I'm learning to think in terms of what makes the most effective strategy, not just which gun does the most damage. So far I've played a little less than 3 hours, and I'm maybe halfway through all of the levels, which means I can expect another 4-5 (after going back to do everything perfectly) for my money, which is considerably more fun per dollar than, say, going to see a two hour movie for $10.

It's not perfect, and it's really frustrating sometimes, but it's enjoyable unique, and that's what I look for in a game. For the price, I have to say yes, I do recommend this game.
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11 of 14 people (79%) found this review helpful
0.4 hrs on record
Posted: April 22, 2014
I played this when it was on Indie Gamestand and liked it quite a bit. The whole vibe is pretty calm and chill. It's pretty much classic tower defense. I love tower defense and while this may not reinvent the genre it's very engaging and fun. The techno soundtrack is nice and I enjoyed the whole package quite a bit. For 2.99 it's not a tough decision...

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8 of 10 people (80%) found this review helpful
0.9 hrs on record
Posted: June 14, 2014
I got this game from a bundle.
I think the game designer put so much thought into this game, especially the bonus stages. It is like a mix of TD and puzzle solving.
A single error can make you fail a entire stage but the game just make you keep trying. Sometimes you have to micro-manage your tower down to every single shot.
Although the graphics are simple, the program has all the elements for a good TD game.
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3 of 3 people (100%) found this review helpful
31.1 hrs on record
Posted: September 21, 2014
I am utterly in love with this game. The music is simply fantastic! (If you're into minimalistic electro/ house, that is.) So far, each stage has it's own colour pattern, looks, sound, and music. The variety has been overwhelming so far. One stage is Upbeat-House, while the next is relaxed Drum & Bass. I love it.

The gameplay is really straight-forward and maybe not a huge game-changer. But the music-creation really adds that extra sense of "Oh god I just placed a new weapon!". Which is one of the best feelings in the game, together with gathering funds and destroying viruses.

It's stressy, yet relaxing. If you're into electronic music and tower-defense games, I'd definitely recommend this!
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2 of 3 people (67%) found this review helpful
0.2 hrs on record
Posted: June 29, 2014
An interesting take on the standard Tower Defense game. Your defense goes by the beat of the music, and the music changes according to your defenses, and how much power you divert between defenses. Very interesting and fun concept.

For example, you don't really have any music playing without defense, or power running through it, but depending on the defense tower set, and how much power you have, the more interesting the music picks up. Keep in tune and in beat with the music to optimize your defenses. A good musical ear helps with planning (make good music) and timing your attacks/defenses (but don't be foolish with where you focus, power-wise), along with a good knowledge of strategy and patience for micromanaging (It's tower defense, it comes naturally). With good enough skill in micromanagment, a good tune might come out of the blue.
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15 of 30 people (50%) found this review helpful
1 person found this review funny
2.7 hrs on record
Posted: April 23, 2014
I gave the tower defense/music game Sentinel another go today, and cleared a couple more levels, but it's really just not my thing. WAY too micromanage-y for my current level of patience, and some of the visual effects that are taking place in the background in time with the music are REALLY distracting (clearly, I am now officially "old"). Maybe I'll give it another try sometime in the future, but probably not…
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3 of 8 people (38%) found this review helpful
0.1 hrs on record
Posted: December 26, 2014
The audio component is unique, and why I initially bought the game, but serves little purpose once the novelty wears off and becomes a bit annoying quickly. Beyond that it's a basic tower defense game, which I like, but an extremely basic one. Normally I'd give it points for that, sometimes you just want a simple game to kill time with, but overall I'd say this game is not that game.
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2 of 7 people (29%) found this review helpful
2.6 hrs on record
Posted: June 21, 2014
Pretty fun tower defense game. Has electronic/techno music. Somewhat rage inducing when trying to get perfects on levels.
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2 of 8 people (25%) found this review helpful
0.5 hrs on record
Posted: October 31, 2014
I normally do not play Tower Defense games, but Sentinel is a TD game I will play and play and play.
Nice blend of game play and music.
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1 of 6 people (17%) found this review helpful
0.3 hrs on record
Posted: December 13, 2014
really cool little game, the music is nice too.
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24 of 58 people (41%) found this review helpful
1 person found this review funny
0.9 hrs on record
Posted: April 22, 2014
Do not buy this game unless you love techno music, and bright lights. By love I mean, have posters on your walls of techno bands, your ipad is 3/4th techno music, and so on. The game doesn't even do that right you look at dubstep and how it has a drop and different pitches, this is more like techno generic song one A, then on to game two remix of generic song one A, and so forth. There is no other music that I came across in my hour of play, and an hour which gave me a head ache.

The music in the game plays no part in how the tower defense handles. It is no surprise that as of writing this the front page does not have a video, for it it did people would see it for what it truly is. If that's not bad enough, the back round on the screen is always exploding in some bright, in your face way with, with sound wave bars, or just odd shapes. The best way to describe this is if you have ever been to a club, stood in the middle of the dance floor, had people bumping into you, as you stare up into a strobe light and let the mind numbing, repetitive remix of the same song you heard the last 4 song melt your brain.

The tower aspect of the game alone is not too bad, it can offer a challenge, and there is a volume slider in the game so you could turn the in game music off all together, and play your own music, but you would still have to deal with the brightness.

At times the screen will also shake, making it feel like your in a boat, or middle of a club, trapped with little air, surrounded by mindless sheep.

The way the gameplay handles, is simple, but never rewards you on winning a match, more of, yup that's nice go away do the next one like a chore. I find it hard to believe even those who love techno music will enjoy this, but no doubt someone will, and be that as it may.
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1 of 9 people (11%) found this review helpful
1 person found this review funny
0.7 hrs on record
Posted: June 15, 2014
Fun, but what is the song? I shazaamed it but it wouldn't identify it.
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0 of 10 people (0%) found this review helpful
0.1 hrs on record
Posted: February 28
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