I've been meaning to read this for years now, having heard so many great things about it.
Ender's Game has been really hard for me to rate. I thought the story was good, a classic sci-fi war novel with a great moral. I liked the characters as they were very believable (for the most part). The science was interesting and I enjoyed that they left most to the imagination. The action was also portrayed well. All that said, nothing really stands out as being "exceptional" when I think back on it. Really good, yes, but not exceptional. Maybe I've been spoiled by more recent sci-fi/fantasy (Old Man's War, Hunger Games).
Overall a good sci-fi story and a fun ride. Liked it.