I loved the movie I was a little weird about it at first, but when I watched it, I loved it.
The only thing I dislike is Sunset Shimmer. She had no back story or anything, she appeared from no where and that was my main question, why wasn't she introduced? Why did she want to take over Equestria... etc
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I absolutely adore the songs though, they are so catchy; I've been singing them ever since I watched the movie xD
The outfits for the mane six are also another favourite, though others may argue of AppleJack being in a skirt I think they actually made it work. Seeing all the background ponies in the movie also made it much more fun, I loved seeing what outfits were made for them.
As ~OnylexOmnyPony said, the movie probably has most hate because of it's difference. I mean I know a few people who go crazy over the idea of humanized ponies or anthro, they see it as wrong. Which is sad, but everyone has a right to their own opinion in the end, nothing can be done about that. If only people were willing to give things a shot (Like myself, I didn't like the idea of the movie at first because I saw the villain and that put me off a little..) ^^;