When I started playing MMO's back in 99 with Asheron's Call, there wasn't a right or a wrong way to play an MMO, you were simply playing a game. You would grind to level up, but hitting that next level was the the sense of accomplishment at the time. Heck even WoW was like that for me for a long time, I'd level by myself, do some dungeons with friends, but there wasn't any "checklist" of gear that you "had to have".
Once Burning Crusade came out, all of my friends and I jumped on the level train and tried to level up as fast as we could, and that was where the wheels started to come off. We still have fun playing together, but the you must to A, before B, and C before D, exposed the treadmill. I quit for a little while and then came back for Frozen Throne, and had fun with that for a while, until we got to the hard core end game.
Looking at it today, or any MMO for that matter now, I only see the game as being about the end game, and not the game leading up to that point. So now I'm forced to grind out levels so that I can then go play the end game content and grind that content and commitment so that I can then do more of the same. Look I like playing my games, I play them as much as time allows, but I have to play on my time, and once I felt like I was forced to play a given way at a given time with a set timing based on youtube how to videos, it started to lose it's fun.
In the end I played WoW off and on for like 5 years, but I can't see myself ever playing another MMO just because they all share the same model that WoW created. For the most part it was fun, but now feeling like it's only a giant skinner box, I can't see myself ever going back to an MMO. Which is a shame because I liked the just playing the game randomly with my friends.