Just say the teaser on youtube and...
www.youtube.com/watch?v=wM8sPzdqyNk
I noticed the human Twilight is in it. This is just pure speculation on my part, but perhaps it's the Twilight who's native to our world, the same way the human versions of Rarity, Rainbow Dash, Fluttershy, Applejack and Pinkie were native to our world in the first film. I'm guessing Twilight (who of course would know nothing of the events from the first movie, since it wouldn't be the same Twilight who came from Equestria) probably transfers to Canterlot High and ends up joining the band.
I'm looking forward to it since I personally enjoyed the first movie, for what it was. (I know there's people who didn't like the movie, which is fine, I respect your opinions.)
I just don't know what went wrong...