As other people already mentioned, I'm positive that the main source of the hate is the humanization of the characters. I often see comments and fan-art that are against the fact that their precious ponies got humanized.
I must say, though, I actually enjoyed the first EQG and it's equal. Sure, a lot of haters might point out that the two movies had plot-holes and stuff like that, but the plot-holes aren't going to take away my enjoyment of EQG.