I was once as nieve as you!!!
Its the biggest game of all time for a reason... I personally enjoy making gold more than anything else, made a fortune last few days and thats not off the cata stuff!
I played WoW for a few years since release. I was raiding in a top 50 EU guild in TBC and I got Gladiator in Season 1 arena, so I feel i've experienced pretty much everything the game has to offer.
These are the reasons I quit:
1) Raiding just became another job. I'd get home from work to spend my time raiding instances instead. Got sick of it in the end. I prefer playing games I can put down when I want to now.
2) They split PVE and PVP gear, so you had to spend time collecting both sets. Made getting items from raiding pretty pointless because you couldn't fully utilise them.
3) Raiding lost the epic feel it used to have in the original game. 40 people running Molten Core or Black Wing Lair is probably my most fond memory of the game.
4) PVP was pretty dire, zero game balance at all, and the balance of power just gets thrown about from one patch to the next. Blizzard seemed incapable of balancing classes at all. When I was playing had limited battlegrounds available which just got boring in the end.
5) Arena - what can I say? awful. Probably the thing I hated the most about the game.
6) Became too easy to get things. At some point there was a challenge behind the raids and getting decent kit. But at the end they practically mailed it to you.
7) The number of total morons playing the game got on my nerves.
Anyway, as i've said i've played it to death, so i'm not interested in playing it anymore. Once you see through all the ploys they put into the game to make it last as long as possible it suddenly becomes pointless to play anymore.
On a positive note though, because as I said I played for a long time, I think they did do some things very well.
I genuinely enjoyed levelling up my characters, quests/areas were interesting, and some of the dungeons along the way were fun too. The game is also ver well designed with a very high level of polish.