In a game that is so progression based, knowing that all the power you accumulate will go to no useful end can be a real motivation killer. The point of Diablo games has always been to get nice stuff so you can murder progressively more difficult enemies. When there isn't going to be a progressively more difficult enemy, why get nice stuff?
I didn't have any problem with the pacing, somewhat agree on the problem of corridor level design, and again I had no problem with the art style. But some of that is a taste issue where our priorities just don't align.