I enjoyed Bioshock 1 very much, and I am quite sure I will give the sequel a try unless it gets horrible reviews. But honestly, I don't think this looks that interesting. More of the same, except that there seems to be even more emphasis on action. Also, Big Sister? Sounds like the kind of "creativity" that goes into many sequels. Take something out of the original and make it either bigger, or change the gender.
Also, the story that makes Rapture interesting, the one about a failed utopian society, has already been told.
Well, who knows. The game might be good. But I would prefer a "spiritual successor" with a new setting to a sequel.