What makes me more eager for this than the other Bioshocks are the NPCs. This time you're not just a lone guy facing generic splicers, the NPC have their own motivations and don't necessarily have to attack you.
The players actions can actually determine who is or isn't an enemy, that's closer to the RPG-like elements Bioshock 1 was promised to have but didn't deliver. Quite honestly I thought it would be Bio 2 that branched out from Rapture, these type of games can't take place in one location or type of location. It would be like Dead Space always taking place in the Ishimura.