Bioshock is one of those rare games that just gets so many things right - the gameplay, the atmosphere, the storyline, the character development and sense of progression.
This game really should be part of every 360 or PC owner's collection! Bioshock takes a slightly more refined and considered approach to the FPS genre than the likes of (the equally excellent) Halo 3, but don't dismiss it for that. The player really feels like they're living in a real world, with real danger and concequences. The tension that the game creates as you sneak into a new area, screams of the deranged citizens and the towering Big Daddies echoing in the distance, is an experience few games, or even films, manage to achieve so well. The RPG elements throughout the game add to the depth and make the player feel more attached to the character they play. Along with the impressive graphics and the peerless art design and direction, this creates a truly unforgettable world, both bizarre and believable.
Seriously guys, buy this game. Spend your money on something that's worth your time and make sure it goes to a developer that deserves it and encourage more of this kind of entertainment!