It all depends on you, the way you look into them.
Personally, i used to play a MMORPG called Silkroad Online for a period of about 2 years. Even then, i was 2 levels from the maximum level.
Why was it addictive to me? I've met a lot of new people there, i've had fun experiences with them through voice chatting and live gaming.
If you have the time, i don't really think it's a waste, however... when you don't have time, you're wasting your life.
I don't see a really big risk, you should just have a strong character so you can quit whenever you want(which ain't always easy, but i think it's much easier than other, more serious addictions).