Played since 2005, raided in TBC/WotLK/Cata T11.
I know exactly what drove me away from the game, could be summarized as casualization of the game by the ultimate misguided inept aka Ghostcrawler. He is lazy as fuck, failed to generate sufficient content and resorted to rehashing time and again. He destroyed the effort-reward basis of the game by making everything faceroll. He filled the game into an assortment of gimmicks, mounts, pets, achievements; now it is a collection game with an online store to take dumb players' money. Finally he abandoned Warcraft lore and infested the game with pandas, jumpy rabbits and some chinese crap that has no connection to Warcraft whatsoever and has no place in the world of WARCRAFT whatsoever. Every time I think WoW has hit the lowest, Ghostcrawler exceeds my wildest expectations in his destruction of the game and fun.
Broken down by expansions:
Rehashed content, Naxx2.0/heroics, ToC the worst raid ever, faceroll heroics: WotLK
Only 5 levels leveling content, no new continent, LFD, little to do: in Cata
Pandas, all the silliness and slaughter of lore with childish elements, LFD/LFR, all around faceroll game: MOP