Two things.
One thing I'm wondering about is how they'll make it atmospheric. In at least the first BioShock, lighting was a large factor to the game, which was also contributed to the fact that it's, you know, underwater and dark. Either they need to recapture that for this game or change how they make it atmospheric.
Second thing, I thought the first game at least had terrible gameplay. Controls felt rough and I didn't find anything really exciting about plasmids. I really wish they tune up the gameplay to make it more fun to play for the game than for the atmosphere. I don't know if they did that in the second one though.