I played WoW for about three years on and off. I had quit for well over a year before Cataclysm, but tried it one more time earlier this summer. I only played for a month before I quit again. However, unlike the previous breaks I've taken, I have no intention of going back to WoW ever again. For this, I have three reasons.
1.) The fact that I was able to level a character from 1- 85 and get him geared to the point where I had beaten all but one of the three released raids AND had only two bosses left in Blackwing Descent simply felt ridiculous. My first character, that I started back in BC, took almost a full year to level to 70 (of course, I was a total noob, but still). The game has simply become too easy. The whole point to having incredibly difficult raids and a rigourous leveling process (not that it was ever THAT hard, but it was certainly too easy and quick in Cata) was to make the player really work for their rewards and have them feel accomplished when they finally achieved it. Nowadays, a lot of that hard work is simply handed to you. You don't need to heavily research the bosses because the process is intergrated into the system, dungeon ques (although, originally, a great addition to the game) have made it far too easy to advance and get gear and the game even teaches you how to use your class. Now, that last one isn't a totally bad thing, but WoW used to be set up so you could, to an extent, customize the "best" way to do things (dps, healing, tanking, pvp). Yes, there were always the "best" ways to do these things, but it wasn't quite as black and white as it is now. In cataclysm, there is a specific "best" way to do things for each role and its class. All I had to do was look up a rotation and I was instantly doing more dps than anyone else in the group. Does it help with raiding? Yes. Does it take out some of the fun? Yes. WoW used to be a relatively balanced game (I think their prime was in BC/ Wrath) when it comes to difficulty. Everyone could have fun in the game and there were raids/ instances that players of all experience could learn and join in on, but there were also those brutally difficult raids that ONLY the best and most experienced players could beat. That was what I loved about the game and... unfortunately, that has disappeared... at least in my opinion.
2.) I'm not about to say that Cataclysm doesn't have good content. In fact, I completely disagree with that claim. Blizzard has found a way to make questing fun (at least for me). It doesn't feel like so much of a grind simply because their really is a story to each area you quest in. I hated questing in BC and Wrath. It sucked, it was boring and it was a grind. They totally changed that in Cataclysm and that was pleasent, but that's about all they did. Gameplay in WoW hasn't really changed, at all. Not that they need to change it, but they could at least add something new once in a while. Flying mounts were the last big change that really impressed me. Yeah, they added siege warfare in Wrath, but it was sort of clunky and not a whole lot of fun. There was once siege warfare type gameplay that really impressed me, in Cata. Going through the "Harrison Jones and the Temple of Uldum" arc, you get to fly a plane and shoot a turret. That was a lot of fun... but it only lasted like two minutes and you weren't able to go back and do it again. If they wanted to add something so fun, why not make it repeatable?! Anyways, the point is, gameplay has been quite static throughout WoW's history and it has shown.
3.) The last reason is simply monetary, but not JUST because of money. On its own, WoW isn't that expensive, but it consumes time like there's not freakin' tomorrow (except when I played Cata simply because I'd get bored and log off). Not to mention they've started to add a cash shop which is like saying you have to pay monthly for a smart phone AND pay for each individual feature. Although, I actually see WoW's cash shop as evidence that it will someday be free to play (along with the, now, unlimited free trial), but that's a LONG time from now.
I don't really ever plan on going back to WoW (unless it becomes free to play, then I might). It's simply gotten old.