I still need to play through the first two expansions and then get Cataclysm before considering this. XD Playing the game isn't as much fun as playing it with others though, unfortunately.
It's an MMO, so content is constantly updated, basically all you get from the first 2 expansions is 2 races, a class and a place to level. The expansion's are pretty much redundant whenever a new one is released, except to let you actually play the game :).
Anyway, Aside from all the newfags and tryhard WoW fanboys saying that this is a Kung-fu panda ripoff this expansion doesn't seem to feel as serious as the previous. Pandaren were an april fools joke in Warcraft III, as keen as I am to actually play a fat panda tanking big bad bosses with a beer keg, they should have just stayed that joke.
New talent system looks meh, but it does aim to eliminate cookie cutter builds, which I'm all for, having a choice in choosing talents just for what I feel is fun, seems great to me.
Pokemon pet system looks alright, I don't think it will be anything more than a novelty for most players.
A new continent is sweet, brand new place to level in, and now chinese gold farmers get to farm in Blizzard's version of China.
All in all, I'm pretty keen for this expansion, I think I may reroll a monk and spec brewmaster, just for the fact that every class right now is absolutely boring.