The book, written in 1985 by Orson Scott Card and updated in 1991, has been quite popular, and engendered a series of sequels and parallel stories. I have never read any of them, but I just found a copy of this one and will soon be reading it so that 1) I can see if I like it as well as so many other people did, and 2) to see if the movie does it justice.
As for the movie … the notion that the best cyber-fighters in the war against interplanetary invaders, the Buggers, would be children is not one that I really buy. I think experience counts for more. And seeing these children being relentlessly trained by Harrison Ford is not a comforting sight.
SPOILER ALERT: I was way ahead in figuring out that the final “simulation” Ender is subjected to is in actuality the real fight. He’s never actually in it, he sees it all as a giant video game. The reason I figured it out is that the simulation was such a fantastic light show, I didn’t see where they could go from there. It wouldn’t be possible to top it. When Ender learns he had just destroyed a planet, and that many humans were killed in the process, he hates it. He’s a killer, he has the reflexes and the brain to be a killer, but he doesn’t wish to be. And I didn’t really buy the ending, where he finds the last egg from the last Bugger Queen, and takes it away, intending to re-establish the Bugger race. Scanning the Wiki synopsis of the book, I see that much more came after that, including the Queen speaking with him telepathically so that he learns the Buggers hadn’t thought humans were sentient, because they had no hive mind. When they realized that, they called off the war. They were no longer a threat to humanity, but we didn’t know that. It seems to me that if they could have gotten that into the movie, it would have made a lot of things clearer. I can’t really recommend this.