As a preface, I love pretty much every single race on Pandaria...The Mantid are awesome, the Grummles are like the best race ever, but the Pandaren? I hate them. It's not even the whole "LOL PANDAS" thing either, it's just...ugh. They're so boring. They're all so pleasant and goodie goodie. I mean, has anyone seen a pandaren villain? Ever? Has there ever been a quest to lop the head off of Po-Xing-Zhao the Pandaren Raider? Because I haven't encountered one.
Seems kind of far fetched that in an entire race of people there hasn't been a single bad egg, and I know Sha, blah blah, control your emotions, blah blah blah: that doesn't cut it for me. The Hozen don't keep their emotions in check, nor do the Mantid, or the Yongol. It's only the Pandaren. It makes no sense.
Plus I hate their animations. The Pandaren Males are just too bouncy, and the females look so terrible I have yet to even play one, so I can't even speak about their animations. Seriously, they're the ugliest females in the game.
But at the end of day I'm just one dude. I guess...perhaps...maybe they were a success? There's really no way to know without taking some sort of huge survey to see if "we gotz the pandas!" was a huge selling point for MoP.