Full disclosure, it's been quite a few years since I read the book but I still remember much of it vividly. That being said, I really enjoyed the film adaptation. Unlike some (many), it wasn't just the names of the characters/title and some piece of crap that Hollywood put together, for the most part, it stays true to the premise and storyline of the book.
There are of course some changes and many of the scenes don't get as indepth as the book leaving some of them, for want of a better word, hollow, ( I needed to explain some parts to the SO who hadn't read the book) but overall the screenplay does a very good job of capturing Card's world/vision.
The most phenomenal part, to me at least, were the special effects and visualizations. When I first read the book, I envisioned the 'Ansible' battle scenes on a screen much like what you'ld see on the old Space Invaders' video game. This movie took that, and the team competitions a the school, to a whole new, state of the art, level w/ fantastic graphics and imagery.
I'ld give it a 4/5 stars. May not buy it but I would definitely watch it again.