Just beat Bioshock 2 on the PC last night.
Overall, I loved it. The original was easily one of, if not my favorite games of 2007, and one of my favorite shooters of the decade.
The atmosphere is quite simply mesmerizing, and is easily the star of the show.
I really enjoyed all of Bioshock 2, if not quite as much as the original, if only because the atmosphere and world isn't as fresh and novel, and a few things seem a bit dated. I also have a few technical quibbles, with some inexplicable slow-down and long load/save times.
Gameplay-wise though, I appreciated many of the changes. Dual weapon/plasmid wield, new, innovative weapons, excellent new enemies, etc.
I didn't quite enjoy the story and characters quite as much as the orignal, although I realize that's entirely subjective. Still excellent, but not quite as memorable I felt as the original game.
Still, one of the best games I've played this year, and another fascinating trip through Rapture.

