Demi nailed it. This has been discussed so much that I won't bother to fully reiterate, but it probably wouldn't be such a big deal if the stuff they decided to fix and focus on actually made the game better -- the combat is better, sure, but it's a polished turd, and you end up doing it to tedium. The level design, on the whole, is MUCH worse. And, as mentioned, all the intrigue of Rapture is gone -- which might have been a foregone conclusion and hence the shift in focus to begin with, but if those levels are all they could come up with, they could have never replicated the atmospheric draw of Bioshock anyway.
I hold a lot more ire for the game than it's probably worth, but I still felt like it was an aboslute waste of time. Wait for Infinite.