The plot of this novel is Harry Potter. But worse. In many ways, Harry's life is a nightmare - at the age of fifteen months he loses his loving parents and is inches from being killed himself. He spends the next ten years unwanted, neglected and abused. Hogwarts and the Wizarding world seems like a paradise at first - he's free of the Dursleys, he's rich and powerful and famous. Except that there are people out to kill him and the Wizarding world is as petty and prejudiced as the Muggle, and a lot more dangerous.
Ender's world is worse. Like Harry, he's unwanted at home, where he's tortured, and his classmates tease him. Except that Ender has to contend with his sociopathic older brother instead of a spoiled cousin, and he's teased because he's a third child in a world where families don't legally have more than two. He was born from government fiat. "Thirds" are despised and fair game.
His talents are recognized (after he kills a boy) and he's sent to a special school where they will be honed.
Harry was eleven. Ender was six. And while Harry has friends and parental figures, Ender has followers and distant teachers who push him along and isolate him. And lie to him in a way that makes Dumbledore look open and honest.
By the time Ender is eleven, he's destroyed an entire sentient race. At the time, he believes it's a game. (He's also killed another boy, unintentionally. They don't tell him that, either.)
Harry will be eighteen when the series ends. And although he will have to kill Voldemort, he will know what he is doing, and one hopes no one else will die. And he will have friends by his side. Ender was alone.
And that climactic chapter. I cried.
(And then there's all that odd eroticism, as when ten year old Ender sees the beauty in an eight year old boy's childlike body. Which was just skeevy.)