Here is an enlightening review by Orson Scott Card, political commentator and author of Ender's Game. There are no major spoilers, either.
http://hatrack.com/osc/reviews/everything/2005-09-30-extra.shtml
A brief excerpt:
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"Well, guess what.
It's great.
I'm not going to say it's the best science fiction movie, ever.
Oh, wait. Yes I am.
Let me put this another way. Those of you who know my work at all know about Ender's Game. I jealously protected the movie rights to Ender's Game so that it would not be filmed until it could be done right. I knew what kind of movie it had to be, and I tried to keep it away from directors, writers, and studios who would try to turn it into the kind of movie they think of as "sci-fi."
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And this is as good a movie as I always hoped Ender's Game would be.
And I'll tell you this right now: If Ender's Game can't be this kind of movie, and this good a movie, then I want it never to be made."
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Good review. However, the projected final box office total is $26 - 28 million (per Box Office Guru). Where are all the Firefly fans? We aren't showing that good SF sells.