Cataclysm in no means "tanked", but it is considered to be the worst received expansion, even by Blizzard themselves, admittedly because they spent so much time revamping the older zones that there wasn't the expected amount of content in the end game.
I phrased that wrong. While the expansion itself didn't tank, it managed to lose Blizz around 2 million subs and was generally poorly received by critics and players alike after it came out. That's not the way you wanna do it as a gaming company.
But this isn't really on topic. *cough*
I haven't read this thread so sorry if it has been said before but my honest opinion on the matter:
Maybe you should have read this thread then. What should and should not be done is out of our hands, but we can voice opinions, yes. Yours is not one that will go down well in this thread, but noted.