I have been playing MMO's since 1999 and yes they can be addictive especially in the early days because it took such a huge time commitment to advance in the game. Thankfully they have gotten alot better at not requiring huge chunks of time at one sitting in order to succeed.

Even with the game not requiring that crazy time commitments of older MMO games some people are still getting addicted to the game. While that is something one should be aware of I would not say because some people get addicted everyone should stay away. For myself I have gotten my kids involved as it allows us to play games where we work together as a team to beat the game. This is a refreshing change from most games that pit you against one another. There is also a social aspect to MMO's that attract alot of people. Clans or guilds develop and friendships are formed.

So there are lots of positive aspects to playing MMO's and to only focus on one negative aspect that the majority of people don't suffer from would be a disservice to a great type of gaming.

EDIT: Btw I am glad you saw it starting to affect your life and stopped playing. I myself was in a similar boat years ago and had to do the same thing. However since then I have learned to balance my life and to not allow MMO's to grab me like they once did. I would say I spend about 10 hrs a week playing now versus 60+ back in the day.