I have done my tours in some major MMOs (WoW, EQ2, CoH/CoV, Lineage, Matrix, etc.) but eventually got bored and hadn't played an MMO for at least a year or two. I finally went back into CoH last month for a few weeks, just to examine it again (I think I left around Release 9 and now they are up to release 18)... but it just expired and I might or might not renew.
My issue is typically this: I like the freedom of playing solo but I get bored playing solo; meanwhile, I like hanging out with people I know and doing things with them, but typically we're scattered all over the country and can't coordinate times, and I waste a lot of time doing nothing while waiting for people to show up.
PUGs were about the best median I could come up with, but those become a grind and I don't know the people I'm with, but I like knowing the people I'm with.
I'm sort of back into just solo PC games, if I'm going to invest time in something. I dunno. Maybe if I was like some of my other friends and had an actual local group of friends who played at certain scheduled times that I could handle, then that would work for me.