I think a lot of people just couldn't deal with the theme. It was pretty much the brightest-looking one yet.
I still don't understand why people got so butthurt about "pandas" and stuff. People asked for Pandaren for years, and suddenly they didn't want them anymore? It's pretty stupid. And don't tell me you didn't, I clearly remember it on these very forums you're complaining about it at.
People just want boring mountains with dragons, bland deserts or desolate snow fields. Apparently that never gets old.