I play WoW also. However, I've played since Closed Beta and I've nearly burnt out. I go on bored streaks where I don't play it for like 1-2 weeks. But it is an awesome mmorpg. I think Asheron's Call is really good too, but then it was the first mmorpg I ever played.
Tried MU online, and it was alright. Guild Wars was good for the first 2 weeks, but became repetitive and extremely boring. City of Heroes was just like Guild Wars...kill this, now kill that. Ok done with killing that, so here's a quest to kill this. All that game consisted of was killing nonstop. After the initial "oh cool I'm a super hero" feel wore off, it became boring.
There is a whole list of mmorpgs that I've played, pay to play and free, but I think so far WoW and Asheron's Call are the best.
Sorrow and pain eat away at my soul yet I embrace them and wait for the end...