I first read Ender's Game in high school and the book instantly became my favorite and fifteen years later it still is. The story is set fifty years after The Buggers attacked earth. It was saved by Mazer Rackham who, almost accidentally killed the buggers queen. Humans, afraid of another attack from the buggers are now searching for another general to lead them in the next battle against the buggers by taking genius children from all over the world to the battle school, an orbiting space station where they are trained in every type of battle.
The smartest of the children in the school is Ender, a third child in a world where parents are usually allowed only two. The bulk of the book takes place in the battle school where Ender and many others are trained to fight though various games.
The most important of those games is a zero gravity wargame where ender and those put under his command fight in zero gravity in games which are increasingly rigged against them, yet Ender manages to continue to win, containing to cause conflicts with others who envy him for being promoted to commander early.
Struggling with the stress he also becomes involved in a virtual reality video game which examines his mental state telling us far more about Ender than even he understands.
Ender's game is ultimately a book about children which captures their personalities perfectly, and not just Ender, his family, his friends, even his enemies all seem both like real people but also real children, and as the sequels in both the Ender's game and Ender's Shadow to read more about both Ender and the other children.