IGN have interviewed Jon Chey of Irrational - a snippet is below...

IGN AU: At various times in its development, the game has been described as an RPG, a shooter, a sandbox game and everything in between. It's obviously one of those new-fangled genre-mashers. In your words, describe the gameplay mix for us - is it mostly blasting? Much puzzle solving?

Jon Chey: Actually, this is pretty simple: BioShock is a shooter. It's true that it is doing things that no other shooter has done before, and that gets people confused about what genre it is. It's funny how genres work. They certainly help people figure out what games are and help them decide whether or not to pick something up and try it out. But at the same time, they often act like straightjackets. Developers get lazy and just follow conventions. I mean, why does every shooter have to go in a straight line from where you enter the level to where you leave?