I'm about halfway through the game, and what do you know, it's more BioShock. It's extremely similar to the first one. Even though it's made by different developers, it still has the same awesome atmosphere that the first game had, and it's not a bad shooter either. Certainly not the best, but the plasmids and different ammo types make it unique if nothing else. The story so far isn't the most interesting. It's not bad, but it hasn't hit me with a would-you-kindly like twist yet.
I say don't expect to be blown away by it. It's certainly not leaps and bounds ahead of the original like, say, Assassin's Creed 2 or Mass Effect 2. But they went and made them some more BioShock, and didn't fuck it up, so if you liked the first game I'd recommend it.