Quite possibly the best game ever created.
The level of strategy required to play this game is nearly incomprehensible; I found myself having to have a piece of paper nearby just to draw out budget plans, and that's not even touching the complex combat system. When combat occurs, there's a sharp balance you have to hold between managing aggression and doing damage; less attacks per second to keep an important character safe, or more to finish him off but maybe propel the alien into your school? It's very difficult to the point that survival horror comes to mind as a genre.
The budgeting system is intense. Allocating funds between fish and weapons borders on art instead of strategy. Don't walk into this game expecting a casual experience. Without spoiling too much, I'll say that the upgrade mechanics are also amazing. While it's usually linear improvement, expect stellar new graphics and sounds along with your stat buffs. There are upgrades for fish, weapons, food, and more that I won't mention.
The soundtrack in this game is absolutely killer. Seriously. It's amazing. You could sleep to the calm tracks, but I can personally vouch that when PopCap wants to build suspense, they build it. They then deliver. Hard. The enemies you'll be fighting in this game are, as previously mentioned, no joke. Those linear upgrades I mentioned are less upgrades and more a scrabble to keep up with the standard of ten steps behind the enemy. Good luck accomplishing even that. And believe me. You'll be pounded with sick beats the whole time.
The cast in this game is great. Deep, dark, thoughtful lines and lovable characters, models, and animations make this game truly beautiful and unforgettable. Every death is truly a tragedy. The end credits are mostly comic relief (literally the first you'll see in the entire game), so they lack a bit in the way of factual information. Through my own research, I've found a few of the character actors:
1. The dolphin's sounds were ripped directly from a Soviet nuclear submarine.
2. One of the "hidden" special characters' grunts are from Sylvester Stallone's first role ever. I'm not sure they attained the proper licensing, but it looks like the beginnings of the lawsuit were swept under the rug.
3. The guppies sound like a plethora of different actors, but is actually just Bill Murray pretending to be hundreds of other actors.
4. The final boss is voiced by Bill Murray acting as himself.
5. The last one I could figure out was the carnivores' bite sounds are the exact same sound as the dog bites in CoD: Ghosts. I'm not sure how that happened, but I promise that if you compare them they're exactly the same.
The last thing I'd like to touch on is the amazing graphical expertise that the art department at PopCap has. Genuinely soothing and peaceful graphics put you into a calm state right along with the soundtrack; that is, until and alien shows up and the advanced gore engine tosses guppy shreds all over your tank. The shading effects are also amazing. Shadows are affected by laser blasts and temporal warp shifts (TWSs as known ingame), and you can almost see the reflection in a guppy's eye as her beloved little sister is strewn halfway across the tank by the razor-sharp teeth of an extraterrestrial. When it needs to build suspense, it acknowledges the hardware shortcomings of the time and leaves a lot to the imagination; however, I promise you that when that suspense finally culminates, you'll wish they'd left a little more to be imagined.
This game definitely isn't for casuals or noobs. I'm not trying to be offensive, but I promise that it'll stomp you into the ground over and over, and its version of a reprieve is stepping back long enough to pull on a pair of steel-toes. The only tip I can give is to avoid indecision because I promise that if you falter for even a second, it'll destroy your guppies so fast that your economy will be irreparably tanked. And if you ever try to turn tail and run, you shouldn't be surprised to find some boot laces dangling from your nose. At least you can take comfort in the fact that the biggest inconvenience you gave the AI was having to dislodge its heel from your colon.