Like realistic shooters? Buy this game.
Anyway. You probly all know the storyline by now so ill cut to the chase. The gameplay consists of hiding behind stuff, shootin the enemy, and gettin back behind stuff before you get your head popped off. If any of you have ever been paintballing, you'll get the idea. Its very realistic.
Graphics are amazing, however the physics could do with a bit of ramping up. For example, when you step into a dead body, it moves like its made of cardboard, not 15 stone of muscle and steel. This is the same for any sort of enemy, whether its a 3ft tall Wretch, or a 9ft beserker. However this is the only problem i have noticed with the game. As for other people saying that some of the sounds the characters make are limited...anyone who judges a game by what the NPCs and your character says...well...enough said i think.
People that are comparing this and Halo...i dont think its possible. Halo is an FPS, this is a TPS. Halo is a fantasic game, and I would say just as good as this, and this is definatly as good as Halo. But then they are different types of game. Saying that this is a "Halo Killer", is like saying this is a Need for Speed killer. Overall i feel that this is the best sort of game (TPS of course ;D) in its category, and a must have for any Xbox 360 owner. Halo 3 will be an interesting release...