I can't say I've met anyone who read this book and hated it. Which cannot be said for a lot of popular fiction out there.
As much as I love Ender's Game, it's its sequel, Speaker for the Dead, that really gets me.
Hanging with Brother Card at BYU-Idaho, November 2007. Yeah, he's LDS.
Be warned: if you read Ender's Game and decide to tackle Speaker for the Dead, remember that Speaker is an entirely different book. The things that you will end up loving about Ender's Game will be absent from Speaker. And be warned also that there are two (technically three*) books that follow Speaker. So if you want to find out what happens to the characters you will undoubtedly grow to love, you will need to read all four (five) books.
OSC is an interesting writer because he uses a science fiction setting not only to tell a great story but also to explore philosophical, psychological, emotional and moral dilemmas that don't exist in our world today. Which I think is a pretty rare thing to find in sci-fi nowadays (although it's abundant in classic sci-fi). And the characters. You fall in love with them. You wish you could be friends with them. You feel sorry for them; you cry when they do. And not all of them are human. When you start to sympathize with beings you know are not human -- I don't think you can develop more convincing characters than that. No sir, no ma'am.
*There is an enormous gap of time between Ender's Game and Speaker. OSC recently wrote a fifth novel for this series that bridges the gap between these two books. Even still, it's better to read them in the order in which they were published, not the order in which they occur chronologically.