9. Levelling
This is an issue I have with close to every MMO game, levelling your character up. If you can't be bothered to put enough content in a game to make it worthwhile the monthly price, don't make it more and more difficult to level up. Having to spend a few hours killing off a certain amount of monsters to reach the next level only to be told I need to do exactly the same but kill 10 more of them to go up another level is nothing sort of absurd. Come on Blizzard, you're rolling in the dough you can afford to hire a few more writers and developers and add in some more interesting content.