I've Done This Before
I went back into Rapture with mixed feelings, and left the same way. I didn't go in with the expectation that the sequel would triumph over its predecessor, but I have to say I'm mildly disappointed with the game. Being a big fan of the original, BioShock 2 came across as sort of a "build-off" rather than a completely new game. Sure, the first game is a really hard title to top, but I just felt like something was missing, not sure what though. I had fun playing it, and I guess that's all that matters, but it lacked a certain something that made the first game so special.
From a technical standpoint not much has changed; it looks just like the first game. I don't mind that much however, because I really like the Unreal Engine and most of the games that have been built on top of it. The game runs smoothly in DX10 on Windows 7 although CrossFire support seems to be lacking or broken (if anyone has information on that please let me know). I didn't really have any issues with framerate but then again the engine is starting to show its age; doesn't require very powerful hardware. Overall, the game is very stable so I would recommend playing the PC version.
On to the game iteslf, I found the story to be less intriguing than in the first, but it was enough to keep me interested. I liked the new weapons (drill is amazing) and the new enemy types; fighting the big sisters can be challenging and fun. The level design was original, as in the first, but some areas felt a bit claustrophobic at times, especially since you're in a hulking suit of armor/dive gear. The plasmid/tonic selection is good with the exception of some that I felt were unnecessary, but it's nice to have options I guess. I had a lot of fun planning attacks and defending the little sisters. I usually don't like spam-fests but the amount of chaos that can be created with a few plasmids is downright satisfying.
So as a whole, I can recommend BioShock 2 for players of the original game, but I might warn them of its shortcomings first. My biggest grudges are it's shorter than the first, the story isn't as notable, and it lacks overall originality. It's a good shooter underneath but is ultimately less memorable than the 2007 original.