by far my biggest issue was when they trashcanned the pvp gearing from MoP/WoD
then the do every single quest in the game and repeat it til you hate 10 rep grinds pathfinder for when you no longer want to play anymore
hated that they got rid of tier sets in LFR (and everywhere else)
hate the borrowed power systems
hate that they got rid of justice/valor/tokens for bad luck protection vendors