I was infatuated by WoW when it came out. I played 2 years straight. It was like a dream comes true. I remember me getting to Ironforge for the first time after finishing the starting area. That was a great WOW and there were still so much to discover.
Eventually, I felt like I've seen everything I could in the game and it stopped being as engaging, and that's when I stopped playing it - I still think, that this is MMORPG done right, others try to innovate, but Blizzard did too good a job so nobody was able to surpass that.
I tried a few other games after that but they never felt quite as good as WoW once did. I'm not playing any MMORPG right now and have not been for awhile (one / two hour sessions to try yet another mmorpg do not count)
On a side note D3 is not an mmorpg, but I keep playing it on and off since launch - I think it's a great game.