I don't consider it having done anything worse than previous expansions.
It just didn't innovate enough to keep my attention, I was getting burned out on WoW, and the expansions starting with cataclysm looked more and more alike.
BC - hey, it's an expansion, that's new!
WotLK - vehicles and phasing!
cata - the 1-60 revamp was pretty cool, but as far as endgame....
pandaria - umm....pet....battles?