Part of the reason is that Blizzard has, for a long time, been rather against making Panderen a full race, despite a fair number of fan requests for them. Now that they've decided to put them in, after subs have started falling, it's just feels like... I don't want to say it. Nope. Not gonna.
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Fine. It feels like pandering.
There are other reason. The whole, "can join either faction" thing seems to ignore all that "recognise race/class by silhouette" they've worked on. Sure, you can still recognise race/class; just not weather or not they'll be trying to kill you.
Another thing is the addition of a new class. I know people will always be asking for new classes, but Blizz had a massive problem getting 9 both remotely balanced and equally useful. Putting in a 10 seriously messed stuff up, and now the impression is that they'll keep adding stuff.
And then you've got to question why they chose to visit this area which had been largely nonexistent in the lore and which seems rather unexciting compared to possible expansion locations like the Twisting Nether (which we were suppose to reach after BC), the Emerald Dream, and, well, those are the only two I can think of, other than maybe Undermine, but they still seem like much more sensible choices than Pandaria.
Basically, half the stuff in this expansion scream "Jumped the Shark" to me.