I thought that many aspects of the storyline (such as Sunset Shimmer framing Twilight) could have been interesting but were rushed. I also thought that Snips and Snails were very out of character, they actually enjoyed being turned into demons and were generally evil, in equestria they were just dim-witted and gullible. Overall, though, I enjoyed the movie and I am very excited for rainbow rocks
Actually Sunset Shimmer was already in the human universe and just went to Equestria to steal Twilight's crown. Pinkie Pie also states that Twilight's counterpart lives somewhere else (I cannot recall the exact line at the moment). I do agree with your other points however