I'm loving MoP, for the most part. A lot of dailies to do if you're a raider, but once you hit revered you can go at your own pace. Lots of achievements done, all reps at exalted or revered, all of my professions are done including all of the cooking ways (two more friends to get to best friends and I'm done). I'm 6/6 N Mogu'shan vaults, 2/3 HoF. I've barely touched the pet battles but so far they've been fun and a lot of people in my guild are very into it. I'm just starting arenas this season and I'm about to start levelling my alt from 85 to 90 now that my main is getting geared and I don't have as much left to do.
Other than that, the game is beautiful (their artists and programmers are wizards with that engine), the music is stellar, the raids are a perfect difficulty for a 2-3 night a week raider, the quests are much more varied, the dungeons are fun, I like the cross realm zone features and the scenarios, and the story integration is top notch. It's a great expansion. It's like they took lots of the good thing about BC, Wrath and even Cataclysm and mixed it into a bowl.
By the way, Blizzard is selling
MoP for $20 on Nov 22, Black Friday through major retailers. You can get everything from Classic to Cataclysm for another $15. Yes, that's only $35 for all
of WoW. If you've never played but always wanted to, or you quit during a previous expansion and are thinking about coming back, now is the time. No I do not work for Blizzard.