It's nice to see other people picking Bioshock, which I have to go with as well. It's tough for me to gauge how objectively good Bioshock is, because as I played it I realized once and for all that I do not like scary games at all. Bioshock wasn't super scary, but it was always creepy, and I didn't enjoy it.
However, I think my distaste for it is based on more than just that. The story is cool, but the fact is that you're not even involved in most of it because it all happens before you show up. And I think the gameplay is weak--there's a lot of room for experimentation and different approaches/plasmids but as far as I could tell no point in really exploring them. I guess I just got sick of all the respawning screaming lunatics I had to deal with over and over again.