WotlK was the beginning of the end, i couldnt bring myself to play it. While the content was at its best, the game had already lost the sense of difficulty and the feel of an MMO. The welfare epics were real, they really ramped up the whole idea that once a tier of content was no longer the most recent the gear was shit and nobody ran it - Gear score was such a bad idea also.
For me, as good as the content was, as well as they made the encounters the rest of the game had already turned the corner and become not worth playing.