I have a love/hate relationship with MMOs. I love them, but I either get bored inside two weeks, or I realize one day a couple of months down the line that my free time is 99% playing my current MMO, and the remaining 1% is watching/reading stuff about my current MMO. At that point I quit in disgust and stay away from the genre for about a year or two.
I put this down to my completionist personality. I need to do everything in a game. Every time I played Mass Effect, I explored ALL of the planets. ALL OF THEM! Even though I knew it was pointless. Even though I really didn't want to. But I had to do it. This translates poorly into the MMO sphere, where every game is built around timesinks. It's even worse with daily quests/activities, where I start to feel guilty if I don't clear them every day.
However, the problem is that I genuinely like MMOs! I enjoy the big open worlds, the emergent social gameplay, the feeling of camaraderie when dealing with group content, or even just playing solo with the knowledge that you aren't really alone there.