Well, I played EQ for four years. I don't know anyone, myself included, that continued having fun after the six month milestone. I stuck around mainly for friends and what-not, had "uber" items and was in one of those high tier guilds. You know why I quit? I realized it wasn't fun.
It wasn't just me feeling that way. I know well over a hundred people that said they didn't really have any fun anymore, but they couldn't stop playing because they already had so much time involved, or they wanted to get into that one guild, or they wanted just that one AA skill, or they wanted to master all tradeskills to make the ultimate item, which no longer was ultimate after the latest 6 month expansion which was $30 for a damn download (nothing like making shitloads of cash charging the same amount as a store-bought expansion that doesn't require packaging, distribution, or even heavy advertising with the 400k+ playerbase that will have to get it just to keep up and play with others).
The thing with EQ, UO, et al is that they start you out with a repetitive set of actions that eventially become a conditioned response. It is a prime example of behavioral modification. Keep killing, get that XP and ahhh mental stimulus, level! The fact that in EQ you hear a DING when a character levels is almost like a cruel mocking reminder of the Pavlovian experiment involving the dog and the dinner bell.
I know not one person that ever thought the games were fun after six months. I played various MMO's for five years and watching the effects it had on myself, my friends, and many other people in the game, I feel quite justified in saying this: MMO's are not fun- they are work and can lead to compulsive disorders.
They don't call it EQ 'Evercrack' for nothing!