The general curse of an FPS game is lack of plot and Sanctum is very scarcely different. It will relay a comic book-style preamble before every encounter but you will mostly find yourself more worried about the map layout of the upcoming battle than the story itself and in the end I think most peopel aren't going to know the story behind the Core Guardians at all. Though those of you who do, aren't going to think it's anything to write home about - I didn't anyway.
Gameplay & Controls: 5/5
Assuming you're using mouse and keyboard (because why would you use a game pad for a FPS...?) the control setup is what you might call standard, but it's called standard for a reason - it works. The pace of each map is always scaled perfectly in my opinion and each time you start a new encounter the difficulty scales well, whether you're playing with friends or on your own. I will say Sanctum will test you - even if you're the type to hunt up tower placement strategies with a little Google Fu you're still going to have to be up to snuff with your shooter skills - Sanctum 2 will send enemies that will reflect fire, take several minutes to take down, and can even destroy your towers from multiple directions. And while it's easy to predict what comes from where and what you should have readied in defense, a lot of the time the enemy AI isn't static. Which is a good thing. No stale battles here!
Music & Sound: 4/5
While the menu music is a bit of a snooze the in game battle tunes really set a mood well - prog electro and D&B compliment Sanctum's futuristic theme perfectly. There are times with REX you will have to endure a plethora of stacked explosion sounds however as well as some of the tower and enemy sound effects.
The biggest gripe I have with how the game looks is in a few of the stages the lighting will be so intense it will seem like you're trying to engage in a staring contest with a star from 5 feet away through a magnifying glass though the environments, character and monster designs and weaponry of the game are beautiful. The menus and maps are nicely done as per the theme of the game though foregoing things like grass and physical damage for textures is a bit of a letdown, it's not too terribly noticable.
Sanctum is a very unique blend of first person shooter and tower defense, and the first of it's kind even. There are even some bits and bobs of RPG thrown in there with the games leveling system, though they work really well. If you've played the original you'll note how much has improved in the series thus far and that gets a major amount of respect from me (mainly because I made the mistake of playing the second installment first and had to backpedal into something I felt really couldn't match up.) The highly customizable pre-battle outfittings and DLC maps and overall difficulty of the game (which can be augmented with Feats of Strength, which are kind of like handicaps and modifiers to make the difficulty even more trying) make it one I can constantly play over and over again. I would definitely recommend this to anyone looking for a different kind of shooter.