It has already been said...
...but Bioshock is amazing. Beyond what the critics say it is the voice of the gamers that should be noted most of all. It is hard to find many who didn't like Bioshock and out of the few who didn't it is even harder to find any who can coherently convey why they didn't enjoy the game.
The game provides a unique and grotesque narrative that covers everything from Big Brother, Big Business, governance, and the tragedy of being human and powerful. A lot of paranormal activity is tossed in which makes the game, on a mechanical level, both feasible (such as plasmids) and entertaining. While Bioshock would not be very notable if it were a stand-alone novel (without any game attached to it) in game format, as a fully realized world, Bioshock is amazing.
The game also has a lot of creative uses of its super-powers, plasmids. The developers really spent a lot of time making them all feel unique. In most games where you have a lightning power it does high doses of damage to enemies. In Bioshock it serves as a stunning attack and it looks great too. The dynamic lighting, the idle animations and the way the lightning leaps from your hand to your target are all done with finesse that a lot of games lack. This can be said about nearly all of the plasmids in the game, really... and on a personal note, I never get tired of watching an enemy get engulfed by flames using ignite.
Furthermore, the weapons in Bioshock, while not the most interesting or inventive, do manage to feel unique from one another... yet somehow stale and bland. Hopefully in the sequel we will see some more interesting weapons.
Apart from the weapons though, this game is a blast. If you play it you will find yourself unable to let go of your controller. The game is too fun to stop; only when extreme fatigue has set in will you be able to save and sleep. Definitely deserving of its 2007 Game of the Year awards that so many have bestowed upon it