Hating and prejudices aside, this is honestly the least I've enjoyed an expansion. I'm just not feeling it. But as you can see, some people are loving it. You pretty much just have to try it for yourself and see if it's up your alley. But a few basic overviews you should be aware of:
1. It's a much lighter theme than previously. The Horde vs Alliance war will pick up eventually, but so far it's pretty tame in comparison to places like Northrend or Outland. The majority of the leveling has much more to do with learning panda culture and fighting their ancient enemies than it does Horde vs Alliance, so again, you'll either love it or hate it, but nobody can tell you if you will. Just be aware it's going to have a much different vibe than WotLK or BC, or even Cata.
2. I don't know what part of the game you focus on primarily, but the PvP side of things is pretty lackluster. The two new BGs are certainly better than the two we were given in WotLK, and aren't direct copies of old BGs at least, but I can tell you now that they won't lead to very many close, epic games. It'll be like Gilneas, where one team establishes an early advantage and the other team can't do hardly anything about it because it's too small scale. I'd say, more than any old BGs, these two will be won by number of healers. To be fair though, Blizzard did say they're wanting to change up queues were teams have an equal number of healers, so that'll help the PvP experience as a whole significantly.
3. Unless you like Farmville, or are immensely interested in panda day to day life, you'll probably want to skip Valley of the Four Winds. It's a pretty awful zone otherwise.
4. World PvP is back. I love it, personally, but some people are so upset over it that they're threatening to quit. So be ready to be ganked if you start a monk and get to questing with it.