I've been eagerly awaiting this movie since it was announced like 15 years ago, so, there is no way I was going to not be disappointed with it. Even if it was a faithful and complete adaptation of the book I would still be disappointed. Still, I thought it might not be terrible and definitely worth seeing. I wasn't as disappointed as I thought I would be, which is probably the best this could have possibly turned out.
The switch to teenagers from children is understandable, and didn't take away too much from the film. The main reason it's been in development for over a decade is that, while it might be possible to find one or two child actors capable of playing these characters, the 20 or more actually needed was logistically impossible. This movie wasn't getting made until someone said "fuck it, they're teenagers now."
I also liked how Bonzo was really short. It made sense for his personality. I could imagine him being taunted for his size when he was a Launchie and resolving to never let anyone push him around or make him look bad. Also, the fight in the bathroom, the part where Ender said "I could break your arm right now" in the same tone Peter said "I could kill you like this" near the beginning was awesome. When Bonzo was in the infirmary after the fight, I noticed something funny. It looked like the machine was repairing occipital lobe damage. The impact he sustained at the end of the fight also likely caused frontal lobe damage as well. Frontal lobe damage often results in personality changes. I could imagine the doctors saying "wait, lets not fix that yet. Maybe he'll be less of a dick now."
Including just enough of the fantasy game to establish that the bug queen was using it for communication and to reference The Giant's Drink was probably the best way to go about things without fully hashing it out and spending too much time with it. I wish they would have also shown Peter and Val trying to take over the world just enough to establish that it happened.
As for what I didn't like: The Full Metal Jacket
references were very tiresome.
There probably won't be a sequel at this point, but the movie didn't leave a lot of options for adapting the existing novels. Completely ignoring the Peter and Val subplot doesn't really allow for for the Shadow
books, and the FTL drive and that the ansible has a limited range for instantaneous communication really screws up possibilities for the original sequels. That, and most of the other books are different and don't make for good space-battle movies. The Shadow
books were far more politics-based, and the original sequels were-- whatever it was they were supposed to be. It might be possible to Speaker for the Dead
by changing the plot significantly and using all the books for source material. Apply the political unrest of Earth to the new colonies instead, have Peter unite the colonies instead of Earth, and have this happening at the same time as the stuff on the planet with the pigs who become trees when they die, and have some space battles and stuff.