Since there is so much negativity in this thread lately I'm going to post some positive thoughts! I resubbed a couple months ago after quitting shortly after MoP launched. I'm really enjoying everything and I have no shortage of stuff to do. Between LFR, Flex, achievements, pet battles, and pvp I almost feel like I have too much to do. I have also really enjoyed the storyline as I've done the legendary quest and went through the various raids on LFR that I never did. Flex is awesome, by the way, and I love the fact that my smallish guild can do (slightly) more challenging content with whoever we happen to have online for (slightly) better rewards.
I'm also really looking forward to WoD. Is it more of the same? Sure. But considering I'm really enjoying what we have now, I don't see any problem with having more of it.
I guess I should add the caveat that I'm an extremely casual player: I only have time to play 30 minutes to 1 hour maximum on weeknights, and on the weekends I might play for 3 or 4 hours at most each day.