I've made it up to level 87. I've completed the first two zones, Jade Forest and Valley of the Four Winds, and am midway through Karasang Wilds.
Valley of the Four Winds
I really liked this zone. It's a pretty quiet zone that reminds a lot of Nagrand. Blizzard did an excellent job showing off the Pandaren daily life. Lots of interesting characters and situations. Plus the training montages were hilarious.
The farm at Halfhill market is really neat. It's a very simple mini-game, but it is very nice to slowly build something, to plant seeds and then harvest a crop. I think that's a mechanic which could stand more use. I'm currently growing carrots, to help level cooking. What crops are you growing?
Blizzard's new quest style is very interesting. There are quests where someone is telling you a story, and you play out the story as that character, as the person narrates what happened. It's an excellent use of the game dictum, "do, don't show or tell". The narration is very Bastion-like, and I find the whole setup just works. It makes it feel that there are other people in the world who are doing stuff.
Now obviously this could be overused, and you end up not playing your character, but random other people. But so far it seems like a judicious use that spices up questing.
So far, Pandaria has continued to impress me. I am really enjoying leveling. I haven't yet had a chance to try out instances, mostly because I join the queue, then get caught up in the quests, then leave the queue so I can continue questing.