Bioshock 2 fixes a lot of the core issues with the original, but sadly doesn't distinguish itself from that original.
Well, here we are with the sequel, and I must say that a good number of those flaws have been dealt with. Plasmids feel more useful. Instead of having to use the independent of your weapons, you use the simultaneously making them feel much less clunky, and more useful in general. Research is another spot of big improvement. The old system had you taking photos that totally took you out of the action. It was a terrible system and has been completely replaced with a much nicer video camera system that doesn't break the flow of the game anymore. Difficulty has been improved a little, especially with the vita chamber disable option in there by default. It still isn't going to get up there on the challenge but I'd say it is acceptable this time round. Also, the game is a bit my stingy with the upgrades and adam this time round, making the choice element more important than its predecessor. So, in the end, where Bioshock was the weakest, Bioshock has taken it up a notch and really corrected that.
So, why not give it a higher score than the original? Well, because it feels like a retread. You get this whole 'didn't I do this' feel to the game. There isn't enough new elements to the game to fight this, and the new elements they did add are underutilized. For instance, the Big Sisters, the focus of much of the press releases early on, is hardly touched on at all in the story. They end up just being another nameless, faceless opponent to fight that just happens to be tough. There is a couple other new enemies, but they too are never really given much spot light in the story which feels kinda unfortunate.
Story wise it also doesn't feel quite up to the caliber of the original. The story itself is fine, but where as in the original you could sorta how Ryan (and Rapture in general) fell from his ideals to the craziness that resulted, this time out Lamb (your chief antagonist) just comes off as plain nuts from the get go. She does have a philosophy, but she's an extremist of that philosophy seemingly from moment one. This seems unfortunate, because it could really have been easily tweaked to allow her to similarly seem like an idealist lead astray by reality rather than just taking the easy route of making her a nut job. Fortunately, while Lamb didn't work for me, I was impressed by other elements of the tale, and other characters, who often came off as more believable and understandable.
Haven't touched the MP, so I'll leave that to MP focused reviewers, but as far as the single player goes, it's a solid and well done game that just lacks that something that lets it stand as new and fresh.