I liked the plot twist because it changed up the way the you were experiencing the game. It's hard to say this without giving anything away, but the combat after you make it to the surface (ha, no real spoiler) gets a little bland though and reminds me of other games. Yes, the final boss fight was bad, but the whole sequence of fighting to him wasn't bad, just annoying because I died SO many times. That was from a gameplay prospective and the ride of watching the final battle was pretty cool.
Funny you mention Bioshock, I saw it being beat a few months ago and it was pretty lame. The final boss fight was played by a guy who hadn't really played the game before and was playing on somebody else's account with most of the special abilities switched off and he still beat it on the first try. However, it must be noted that he died A LOT in his playtime prior to the final boss, too bad the respawn system felt like there was no penalty for dying.









