The most overrated game since Gears Of War.
After I finished Bioshock the first time on the 360, I was left a bit underwhelmed, wondering what all the fuss was about, so I decided to play through it again. As I'd found most of them in my first playthrough, I didn't pick up the diaries left by the characters and I was left to focus on the gameplay. This is when I was finally able to put my finger on what's wrong with Bioshock - it's the incredibly simplistic gameplay. It hearkens back to the original Doom, consisting of nothing more than repetitive, brainless shooting.
Bioshock's biggest crime, however, is what it promised to be. We were promised an emergent emergent world that changes with the player's actions, but in reality what you decide to do has no impact on how the game ends. Then you have the generic story with so many loose ends it's a joke.
If you must play Bioshock, then rent it, as I can guarantee you won't want to play it a second time.