Was a MASSIVE fan of bioshock 1, thought it was brilliant. Started with the single player and I have to be honest, it's absolutly brilliant. The graphics are top notch and the story line is just as good as the first. They made little tweaks to things like hacking to make the game run a little bit smoother. The only let down I had with the single player however was just how long it took to finish. The first one went on and on and on and whenever you thought it was just about to finish, BAM! there was more. Bioshock 2 just does not cut it when it comes to how long it should of been, no where near.
Bioshock 2 introduces multiplayer. I personally think they only made the MP to sell the game on consoles and i'll be honest, it's shockingly bad. It's been out a week so far and it's laggy, buggy and it's a nade launcherfest and I can't really see that changing. I think the novelty will run out very very quickly.
If you like bio 1 and enjoy your singleplay then i'd get this straight away. If your buying for multiplayer then buy it anyway to play sp but do not expect anything at all from MP. Had the foundations for a perfect game but it only get's a good from me.