I think hypes sums up the positive sides of MMO's pretty well but they sure as hell have their bad side aswell. I played WOW pretty intensively for around a year and a half and finally decided to pack it in around 2 months ago, it's not that I stopped enjoying the game but I was coming more and more to realise that the time spent on the game in no way justifys what I was getting out of it.
The game can take up most of your free time if you let it since it is made in such a way that the more time invested in it the more of the higher level content you get to experience.
Also what I really think is the biggest downfall of these games is that once you have started to do something in game with a group of other people and something comes up in real life you'll either have to let down the guys in game or just ignore whatever it was that came up.