Had some classic novel adaption problems. The point of the majority of the story is to isolate Ender. In the book we can hear his thoughts, so we get to know him. In the movie, he's got no one to talk to ... so he just doesn't really talk. Also needed lots of room to breathe.
However! Some pretty impressive CGI in the 3rd act (you'll know what I mean once you've seen it) and Battle School can't be anything but badass.
God, I want to go to Battle School.