I'm into it about three or four hours. Replayability will be high for me, as there is just so much to look at. I keep feeling that I'm missing key features, audio tapes, power ups...
Ha, I'm seriously considering buying a 360 just for this game. And Oblivion of course, because my crappy little laptop would probably smother me in my sleep if I started searching around online for the PC version.
The crappy thing is that, although I could afford the 360 and a TV (I currently don't have one) I wouldn't have any time to play until Christmas, due to school an all. But Bioshock just looks so. damn. pretty.