The true essence of Ender's Game cannot be understood until one simple fact is really absorbed: Ender is a CHILD. At one point in the book, Dink points this out to Ender:
"...you think these people are normal. Well, they're not. We're not. I look in the library, I call up books on my desk. Old ones, because they won't let us have anything new, but I've got a pretty good idea what children are, and we're not children. Children can lose sometimes, and nobody cares. Children aren't in armies, they aren't commanders, they don't rule over forty other kids, it's more than anybody can take and not get a little crazy..."
The loss of childhood is a recurrent theme:
Does it ever seem to you that these boys aren't children? I look at what they do, the way they talk, and they don't seem like little kids.
They're the most brilliant children in the world, each in his own way.
But shouldn't they still act like children? They aren't normal. They act like -- history. Napoleon and Wellington. Caesar and Brutus.
Of course, Card tends not to write anti-utopian fiction, in general; he addresses current concerns. As Card notes in his introduction, children that read the book tend to identify with Ender on multiple levels. I know that when I read it, at age 8 or 9, I was amazed: adults really did act the way they are portrayed, those manipulative bastards! Children don't have childhoods, they have schedules and strictly enforced limits on their personal lives.
I know that I function best when I have a couple of days off to crash once every month or so (aside from weekends). In high school I could do this and it did wonders for my sanity. (And it didn't hurt my GPA too much...) Could I do this in grade school? No. In fact, even on weekends I had youth league baseball games to play. I never liked playing baseball but I was a child and so I couldn't make any decisions for myself.
This is what Ender's Game means to me: Children cannot cope with the expectations of others. Peter and Valentine managed just fine on their own, while Ender had multiple nervous breakdowns. Which ones were ultimately more successful? It's really a tie, though Ender did his best work after the pressure let up.
"Hey! Teacher! Leave them kids alone..." - Pink Floyd