I havent kept up with the production of the movie so far so this trailer is the first time I've seen anything from it, and to be honest it was nowhere near what I was expecting.
I was expecting something more along the lines of a higher budget season finale/opener type of story, that would be inline with other movies from cartoons shows (see Equestria Girls) either catering exclusively to fans of the franchise, or almost ignoring them to try to bring in a new crowd. But this looks like it is neither, and that is great news!
I wasnt expecting such a departure from the original art style, and I'll admit that the juxtaposition between the 2d ponies and 3d back is a little jarring at first, I expect though that it will look much better when the movie is finished and you're watching it. I do really like the way the ponies look and obviously the animation is so fluid its gorgeous!
Basically this trailer had me go from "Yeah, sure I'll watch it." to very excited for it. Needless to say I do have a slight bit of trepidation that it turns out right, but for now everything is looking like it's in capable hands.