My big problem with the multiplayer is that all of the time spent on it could have been better invested in beefing up the single player experience. The multiplayer isn't the train wreck that we got with the attempt to do multiplayer in say "Condemned 2", BUT I think it's simply being more highly rated than it deserves simply for not being a complete failure rather than being anything truely incredible. People have for example mentioned that it's unbalanced (I don't think I've even seen many defenses of it's game balance, which is odd because even the most grotesquely broken games seem to have legions of drooling fanboys claiming any competitive game is pefect, especially if they are winning with things the way they are).
As far as the main review goes (not here directly) reading between the lines, it seems to me that a lot of people in the industry are reluctant to call this game as good as the first one because it's sort of flipped the political message around. Bioshock was pretty much a banner being carried by the left wingers that by and large make up most vocal gamers. "Oh great, they are zapping Ayn Rand, and busting on the conservatives. Take that Bush!" (trust me, it was everywhere). This time around the bad guys are exactly the opposite and it makes some very clever comments about left wingers, grass roots movements, and pretty much the opposite side. Not much else has changed, and actually the game has improved on it's own, so it strikes me as a lot of people are going "ummmm, errrr, it.. uhhhh lacks innovation".
But hey, that's just my opinion.
Bottom line is we'll see what happens with Bioshock 3 if they ever decide to make one. I just hope they set it in the 1980s and find some way to introduce some actual punk into this so called "retro-punk" game. I also hope they just flat out scrap the bloody multiplayer.