Pretty decent shooter (probably the best on the Cube), though not without it's flaws.
The gameplay is fast and furious, but if you try to run and gun your way through, you will not get very far. You control a squad of three other teammates, and for the most part they obey your commands. You can even pick out a specific spot in a room for your squad-mates to move to. They have a tendency to die a lot, too, so don't be surprised if you look around and realize you are the only one left. The guns are cool and have a realistic feel to them, as do the grenade explosions.
The AI is flat-out dumb at times, and decent at best. They will shoot at you a lot, but they don't tend to take cover or run away when you are filling them full of lead. At least the rag-doll physics make them look like they are really falling over dead. I love shooting them out of 2nd story windows and watching them crash to the ground.
I haven't tried the multiplayer, but I'm sure it's good. The Rainbow Six games usually have a pretty entertaining co-op and head-to-head mode.
The graphics are really impressive. Everything has this shine to it, and makes it look nearly as good as the PC or XBox version. The environments have a gritty and run-down look to them, and it really creates a terrorist-like atmosphere. Your teammates and the enemies may not always run around realistically (kind of a robotic, gliding thing going on sometimes), but whatcha gonna do? The game runs at a pretty smooth frame rate with no real noticeable slowdown, but the game will sorta "hiccup" at times when you're in certain environments. It's not that noticeable, but graphics whores might be a little bothered by it.
Overall, this game is pretty good and it's well worth your time if you're a fan of realistic, tactical FPS's. If you are the type of guy who likes more arcade-style alien shooting, then you might not be so impressed. This game is only $29.99 brand new, so I'd suggest you pick it up if you're a fan of this genre.