Novel adaptions into movies are often a hit or miss. Some novels are paced differently than the average film, and Hollywood has budgets, time constraints and script writing to work out. In this case, Ender's Game was a good movie that captured most of the ideals, events and lessons of the novel.
In terms of the scenes that were brushed over, I didn't mind, mostly because I didn't enjoy reading them, but there were a few things that I didn't think should have been brushed over.
Ender's choices are very important, and as the story draws to a close, many truths are revealed to him that affect him as a person. Not all of these truths were revealed in the film, and it's possible that if they were, it may have changed the rating.
In terms of the film itself, I reccomend it to everyone, especially fans of the novel. Like I said earlier, the movie does the novel justice, and in terms of it's rating, I believe it stayed true to the premise of the original story. Even if you're a hard core fan of the book, this movie is worth seeing in my opinion. Some of the best scenes in the film are the battle room scenes, which are amazing and make you wonder how they created them.
In my personal opinion, I had hoped they would explain more of the psychology that Colonel Graff used on Ender, because it really defined an aspect of his character, and showed the internal conflict he constantly faced with difficult decisions.
I can't say more without spoiling the movie for people who haven't read the book. So, I will simply recommend it, along with the novel, if you haven't read it.
There's a reason why Ender's Game is one of the best SciFi novels of our time.