I played WoW for about 2 months, hit cap and found out that all there really was to do at endgame was PVP and raid Molten Core over and over and over and over.
I never did like instances, they seem less real to me. There's no chance of just bumping into somone at random in a dungeon and teaming up to get somthing done or seeing somone else doing somthing else and wondering what that might be.
Crafting was poorly designed. No failure at all. You pick a craft to make stuff for yourself, forget about using it to make money because a billion other people are going to he high level in that tradeskill too.
Money serves no purpose beyond buying a mount and armor repairs. everything is bind on pickup.
There is almost no death penalty at all, so there is no reason to avoid bad tactics or not do stupid things. You can throw yourself against an obstacal over and over untill you get lucky.
I finally got sick of it and went back to FFXI. Comparing other MMOs to WoW is not a fair comparison because they are really two different markets. The vast majority of people who play WoW would not have purchased an MMO otherwise and it is designed with them in mind and not hardcore MMO players. So it's no wonder that the latter get bored and leave after a few months. I have a feeling though that in 2 years WoW will be where Starcraft and Diablo II is now. The people currently playing WoW are not long term hardcore MMOers and will eventually move on to the next latest greatest thing.