I played WOW all the way back in the late Beta era and pretty much regularly till around Wrath of the Lich King, during which time I played a bit but not often till when Cataclysm was released and I stopped playing entirely. No dramatic story or anything, I was never addicted, I didn't lose friends or health. If anything during those years were some of the best times of my life. I travelled a lot and enjoyed myself. After Cataclysm however I just wasn't enjoying the game nearly as much especially with my interest already fading so I simply stopped playing.
So with all that said what was the allure of World of Warcraft? For me at least it was a combination of a setting I loved, a massive world I very much enjoyed exploring, friends that also played the game, and extremely tight gameplay mechanics.
The original Warcraft rts was actually my first strategy game and I to say I liked it a lot at the time would be an understatement of epic proportions, same with Warcraft 2 when that was released and the Tides of Darkness expansion pack. I remember the manuals for those games contained all these stories and character details for the setting as well as the basic game mechanic stuff, must have read those manuals a dozen times each if not more. Then Warcraft 3 came along and that was a blast as well, quickly establishing Azeroth as one of my favourite fantasy settings in gaming.
So when World of Warcraft was released the first reason I wanted to play it and one of the main things that kept me playing was the novelty of seeing all these locations from the games and interacting with them in a way the rts never allowed, and in that respect World of Warcraft was brilliant. Stepping foot into Stormwind for the first time? Breathtaking. Or my first trip into Ashenvale? Stunning. To this day I still think the games art style is amazingly well done and WOW contains some of my favourite game locations to date. Great music too!
That's a large part of what kept me playing anyway. The other two aspects were friends and the gameplay, which while not exactly the most innovative is nevertheless extremely well done. Add to that some extremely tight boss fight mechanics and an entertaining group of companions to fight those boss with and you've a winning combination. Karazhan for example remains probably my favourite 'instance' of any MMO I've played to date, that place was just brilliantly designed with not only fun gameplay mechanics and a clever visual style, but a nice story behind it as well. It's a location that dates all the way back to Warcraft 1 so to finally see it and have it so fun to enjoy, well, that was a treat!
Still not everything can last forever so I did eventually get bored of WOW and stop playing, I very much doubt the next expansion will bring be back either because I genuinely don't give a shit about kung-fu panda. But hey, good times! That's why I played WOW!