I started playing WoW in early 2008. A buddy of mine starting playing because his brother and friends started. I ended up following the snowball effect and picked it up myself. From then until very recently, I played a warlock since the end of BC. I was in a high end hardcore raiding guild and did heroic modes regularly, and obviously raided a lot.
Then came blizzards announcement that the next patch being released will be the end of the current expansions content. It seems that they are really moving on past WoW in my opinion. I ended up quitting for good and have vowed never to play again as long as their focus is constantly tweaking the classes for arena play and not focusing on content.
I also played RIFT for a while too. The way I feel about MMO's is very simple. Their practice of grinding to get to a goal, while a good way to get max value out of a game, becomes a tiring process. It makes the game feel more or less like a chore, its called a game for a reason!