Many people created the meme that it was the worst expansion back then (or at least the worst expansion by a very easy margin and a very clear way) but for me it was very clear that they were biased by the mere fact that back then the overwhelming majority of players that were playing and they were still in the game were players that were there from the start or even the very start and I mean players that were there since Vanilla or at least late Vanilla or at most early BTC and it was the first time that most of them hit an age or a stage in their life that they really wanted an exit from MMO-long hours gaming and they wanted an excuse.
You see: in this game when you reach a certain age/point in your life you often feel the urge to exit it because you want to do something else because it took so many hours/per day in your life and some people are psychologically so attached that they really want a good excuse to do it and they don't have the capacity to realize and understand that they they do it because their own life had a turn and not necessarily the game itself and I've seen that fact clearly in many cycles of the game (vanilla/btc(most players first enter)->wotk(they're still in(nobody wants yet to live))->cata(they get old and leave)->mop(new players)->etc.).