I actually only just finished it the other day, and I found it really entertaining and interesting too. The design and art direction is just beautiful.
If I were to make a criticism, I'd say that the game seems to drop you slightly into the deep end (zing!) with all the various plasmids, items, tonics, hacks, weapons, upgrades, chracters.... etc etc. Maybe it's because I'm used to playing shooters where everything is more clear (read: stupid), but I found the game to be slightly overcomplicated. Then again, this could just be in contrast to Left 4 Dead, which in my opinion is the abosolute pinnacle of advanced simplicity.
All in all though, if you own an Xbox, you need to own Bioshock.