Ender is a child in a future world where having a third child isn't done anymore. But it's allowed as long as he is taken into the military at the age of six, with the high hopes that he is the genius they're in need of to save them from the 'buggers,' or the bug-like alien race that is threatening Earth.
I think what I enjoyed the most about 'Ender's Game' is that it is just as much about the inner conflicts that the characters in here face as it is about saving the world. Ender has to face off against bullies, his own demons and society's high expectations of him constantly, till you think he's going to break and give up.
Everything in here is woven intelligently into the plot which builds up to a great ending. I'll have to pick up 'Speaker of the Dead' to see how Ender's ventures continue, as the ending also leaves much to further explore in this series.