The story basically lacks that massive game changing mind f**k of a plot twist that the first game had 2/3rds of the way through. But i think it actually packs a more emotional punch than the first game and as TJ said the gameplay is improved. I actually find it more fun to play through the second game.
I'd definately recommend the single player DLC. If you take your time with it and explore like you would in the main game it can give you 3 hours of a brand new, stand alone story, that occurs parallel to the main game and its got a great twist at the end (while it might be a little obvious to some it still shocked me). If the DLC is the final farewell to Rapture (seeing as the new Bioshock has taken to the skies) then its a worthy one.
I still hope one day that they make a final Bioshock game set in Rapture. The possibilities for locations are still endless and no matter what people say I dont think id get bored with seeing Rapture again. The same people who will play endless shooters like COD that all have a very similar look, complained about Bioshock 2 just retreading the same ground as the first game? What the f**k? When a location is as brilliant as Rapture why not use it again.
