I'll certainly agree that Bioshock wasn't a terrible game but it had a lot fo questionable ( to me) design decisions that made the game much less interesting.
For example, in SS2 "research" was an entirely different gameplay mechanic than shooting. One can certainly make the argument that SS2's "research" was nothing more than a foozle hunt, but it was still a different mechanic from the shooting and added variety to the gameplay.
In Bioshock "research" was streamlined into a shooting mechanic, only instead of pointing and clicking with a "gun", one pointed and clicked with a "camera".
I'm sure some people think that was an improvement, but for me it was just one of many ways BS went out of its way to be less interesting than its predecessor.