Ender's Game is a book that will speak directly to whoever reads it, for it is about loneliness and specialist expertise - two things that everyone is familiar with in their own lives, in one way or another.
Ender is a young prodigy space battle commander whose adventures through training school make up most of the book. Ender makes friends and enemies, and must deal with life in a world where no-one understands him, except his sister who he never sees because she is on Earth while he is training in space.
The book covers a lot of different topics, but principle among Card's many theses is that to beat an enemy one must understand them completely: one must - in a manner of speaking - love them. This is a powerful notion and one that is explored in detail, with a very emotionally resonant ending and surprise epilogue.
I particularly enjoyed the videogame which Ender returns to throughout the book, where he is exploring an alien planet and battling various nightmarish foes, solving puzzles, and put under extreme emotional strain. It reminded me of the kind of videogames we are beginning to see nowadays (such as Shadow of the Colossus) and I was amazed an author had come up with it so many years ago.
An emotional and intelligent book, for adults and children alike.