it is going to be impossible to portray Ender as it was written.  he was 6 in the story and had a highly complex thought process.  i'm guessing that he will get dumbed down, sadly.  
i looked at the wikipedia page on the movie.  the cast looks interesting.  i've never heard of the kid that is playing Ender, but he is supposedly a great upcoming actor.  i would have been happy if they could have gotten the kid that played voldemort.  
not too happy with harrison ford.  he is too set in his acting to really bring this character out.  to be honest, i'd like to see a dark brendan fraser.  grizzle him up, have him play nice with Ender, and then tear it all down.  it would definitely be a stretch, but it could work.  
mazer rackham should be played by someone a little younger, IMHO.  if they could bulk joseph gordon-levitt up, get him mean, and age him a little that would be my choice.  they guy is supposed to go back in time basically to train Ender.  not excited about ben kingsley.
the other actors seem fine.  abigail breslin as val is a good choice.  
overall, i'm pretty wary about the movie.