The unhappy are always the most vocal part of the community, official forums or here or anywhere (except for WoW subreddit which is oddly positive).
But doesn't it seems to be at all time high? For all types of different reasons people seem to be unhappy with general design of the game.
Back in the days a lot of the complaining was about class balance (certain specs being unviable, others being overpowered).
Now people complain about:
- flying/no flying
- lack of community
- spells/pruning
- everything regarding current state of pvp
- too much focus on raids
- lfd/lfr
- garrisons, gold being useless
- content drought
- still class balance
Off the top of my head, probably missed a bunch more very obvious ones.
Think the problem is everyone knows how much potential wow has, but very few people see it as living up to that (for whatever different reasons).