You know what? I didn't like this book as a kid and I liked it even less as an adult.
The typical response to this opinion is that I need to read the rest of the series before passing judgement. But I plan on judging this book on the merits of this book, not on the rest of the series--nor on the author's more recent antics. So, if you love this book, please go ahead and dismiss my opinion as worthless. This isn't a book where I really want to debate and defend my opinions.
I think, at the core, it's because I'm not and have never been the target audience. How can I tell? Well, passages like the following were a bit of a clue:
"A few girls. They often don't pass the tests to get in. Too many centuries of evolution are working against them."
Scifi doesn't tend to have much of a place for women except as damsels, victims, and tools. In Ender's Game, they fall into the latter two categories. There are two named female characters in the book. Count'em. Two. One is there to be manipulated. The other is there as the Token Female who relies mostly upon informed abilities but is the first to crack under the pressure.(show spoiler)
Did this bother me as a kid? Probably not as much as it does as an adult. But every time I reread the books from my childhood, I rediscover the relentless voices telling me that my gender doesn't belong in science or scifi as anything other than tools and victims.
And then there's the whole genius protagonist thing. I've always believed that superintelligent protagonists are a mistake because they require rather a lot of the author. Card, however, came up with an extremely clever workaround: Ender's story is interspersed with various military leaders commenting on what a genius he is. This is, in my opinion, an utterly brilliant gimmick. Take, for example, the "Giant's Drink" subplot. In the video game he plays obsessively, Ender gets stuck on a puzzle where a giant offers him two drinks, one of which is poison. He plays over and over and over and picks the wrong one again and again and again. And then, after losing an impressive number of times, he attacks the giant, which strikes me as a pretty standard thing to try. But fortunately, our observers were there to tell me that rather than exhibiting a fit of childish pique or trying a natural tactic in a videogame, Ender had been positively brilliant:
"Isn't it nice that Ender can do the impossible? ... What matters is that he won the game that couldn't be won."
The whole book is like that. I was continually amazed by the simple strategies that the observers insisted on labeling as pure genius.
Even so, I think the exploration of preemptive attacks and overwhelming force adds an interesting dimension to it all. Most of the book reads like a recapitulation of Heinlein'sStarship Troopers. Again and again, Card reinforces the idea that it is laudable to retaliate with extreme force against those who use extreme force, and against those who attack first, and against those who might be a threat. But at some point, ambiguity creeps in. And no, that's not to say that the book's message is a pure repudiation of preemptive attacks. The most fascinating thing about the story to me is that Card doesn't really try to turn it into an aesop.
No matter how Ender's Game looks at the outset, it's not just a repetition of Starship Troopers, and that's certainly something.