Everyone and their mum has written a Bioshock review, so I'll try and say something you haven't heard yet. Poo.
The worst parts: -Big Daddies are a little dumb, they walk right into the painfully obvious traps you might set which makes them disappointingly easy once you get the crossbow. It takes away from the experience after a while.
-Vita-Chambers. You may know this one already, instead of re-spawning at a previous time and place you respawn at only a fixed place. So any damage or progress you have made stays done. It is the single worst choice made by the developers and takes a lot away from the danger you should feel being locked and hunted in this city. It makes your attitude so casual you don't mind dying because you know it might be quicker and more resource friendly then having to fight it out with whoever you have p1$$ed off. Yes, it keeps you in the world, but it kills so much of the sense of desperation that the game could and should THRIVE on. Not to mention the fact you somehow are genetically reconstructed with clothes, guns and ammo and absolutely no temporary side effects. I love this game and tried to learn to like this choice but in the end it ends up draining the water from the tub while you're still in it.
The Best Part: I have never felt so enthralled at looking at the walls in a game. I have never taken so much pure joy from hearing the enemies talk when they don't know I'm there. I have never felt a world so complete as I have in Bioshock. This is a city with a past, a heart, a philosophy, people with lives, and of course it is a city with an end. So what makes it so good is that it all adds up. In any other game the aliens attack/you get powers/civil war/great quest, all that provide some thin justification for why you do what you gotta do. Not here, it's not some lame "ok now for the motivation and explanation scene." Rapture is a city that lived and fell without you, its people and history not just support what you are doing now, but make it feel like it was inevitable. That this is a full world and it will progress, with or without some player thinking their character is the center of everything.