Not to interrupt the "I can't afford this so it sucks" flame war, but I have a couple of actual observations after about 4 hours of play last night.
I think a lot of us were hoping this would be to Bioshock what Half Life 2 was to its original, and its not. But that doesn't mean its a bad game, just one a bit less inspired than its predecessor. Less than masterpiece can still be good.
Surprisingly, though, it kinda limps out of the gate. The opening sequence of the original was a classic, and the sequel is going to have issues establishing that same cred at the beginning. I see a lot of "I played for half an hour and it sucks." I can see why. It didn't grab me at first, either. Felt a little shallow, like a third party developer had been given the IP and didn't quite know how to capture the magic.
But by about the third zone it starts to take shape, and gets much more engaging. Rapture is actually quite a bit more detailed in this than in the original. The environment design better reflects its history, and its minute details tell a good secondary story (that occasionally rewards you for paying attention with hints and tips).
A very noticeable failure, however, is the execution of underwater segments. It just plain doesn't work relies on outdated visual tricks. This was a hugely lost opportunity.
Haven't tried MP yet. Not really that interested in it. That may change when I finish SP, we'll see.
So jury's still out, but with lights off and 5.1 cranked, I was deeply immersed and I'm looking forward to going back tonight.