Oh man. I'm really excited by the looks of this.
Preview hereI don't think there's anything wrong with wanting to make more games like this. If you're a fan of a game, then how can you be upset that it's successful enough to justify more games and broaden out the universe a little or take it in new directions? A sequel gives the developers the opportunity to look back at what they did before, look at the criticism and improve upon it, making a better game. Look at games like Uncharted 2? Or Better yet, Assassins Creed 2? Both arguably much better games than their predecessors because they were able to work on what came before.
Don't forget, this isn't out until 2012. Doesn't strike me as strong as Activision ringing all they can out of COD or Guitar Hero. Still a lot of time before you can pass judgement on a game as being a lazy sequel.
The only thing that strikes me as odd is how a freaking sky city is somehow technologically inferior to Rapture. It's like technology working backwards XD