I read the book, and in while this movie would be fine without the book, the parts they left out and the changes in the plot were quite maddening. Many parts were left out or changed and made the movie far less suspenseful. For example, the ages are all incorrect by many years, Bonzo has only a few inches on Ender, and the changes to the armies were constantly stacked in Enders favor. The whole point is that Ender is a genius with all the cards stacked against him, not that he got the most stacked army the entire time.
Outside of this, it was a decent movie, it simply lacked what made the book by Orson Scott Card incredible.