BioShock was designed by Ken Levine and developed by 2K Boston. BioShock 2 is not. Levine is not working on the game. But should you be worried?
The second entry in the BioShock franchise is being developed by 2K Marin and 2K Australia. The BioShock 2 trailer was recently released, and while it doesn't show any real gameplay, it does look promising. Kotaku's preview for the game has been promising as well.