1. The visual clusterf*ck in the melee zone, Goodness gracious, at times you can't even see the damned boss not to mention that your character disappears in a mist of yellow, green, purple and what not colors. Wth were you good people at blizzard thinking when doing that design. Pretty in solo mode, useless in raid groups. At least give the option to turn it the hell off.
2. Linear questing - Mindblowing boring to level more alts after the first time.
3. CRZ - What an half arsed system, nothing good has came from it. If you want to merge server, just bloody do it.
4. Not doing the item squish before MoP. Ending up with higher numbers than the core of wow was designed to handle making instances and raids laggy as f***.
5. LFR/D - I must admit I loved the change in the begining, but it has pretty much killed off a good server community.
6. Flying in Azeroth, this goes perticulary for PvP realms. World PvP *poooof* gone.
7. For the love of god seperate PvP from PvE. I kind of understand why this haven't happen, cost, time and money.
8. Stuns, CC everywhere. Why oh god why did you do that? Atm it looks like they're working on a way to reduce it.
9. Don't ever do an asian theme again, it's pretty but it's not Warcraft.
10. The revamp of the paladin class. Pre cata was the best state of the class imo, cata version of retribution was more clunky then a 1 stroke engine w/o any oil. MoP version was a bit better, but oh god damn so boring. Pretty much what you did was making it into a useless combat rogue without sap and stealth.
This one gets a little section of its own:
Dailies - Oh my flippin' god where do I begin. Too many, too little, mindnumbing boring and the reward for not killing yourself when doing it was well... shit.
MoP could have been a great addition to the World of Warcraft series, but it's pretty much falling short in every single place but one. Raids, haven't been in one raid in MoP that I didn't like, so it's not all bad :0) But the number 1. and 4. on my list makes it not the best content I've experienced.