The book Ender's Game by Orson Scott Card is an odd little thing. It is essentially a book well suited for teenagers since it centers around Ender, the main character, being enrolled in a military school at a young age (7 or 8, can't remember) and struggling with his teachers and classmates. This is with the background of Earth's war against an alien race, and the army's goal of training the next general for their star fleet.
The "game" element is particularly well made. The main game is some kind of laser tag in zero-G, which should be hard to describe, yet the author masterfully makes it easy to understand. A lot of emphasis is placed around the competitive nature of the various teams's matches. Most character development centers around this competition as Ender, being so gifted and smart, rise up the ranks too quickly. Ender's brother and sister are gifted too, but they were not selected for that school and stayed on Earth (Ender's school is in space for the zero-G).
Which brings my main gripe about the book: While Ender's and his siblings' "genius" is an important plot point, it still feels like a cheat that they don't really talk or act like kids. I've seen that trick used in comic strips (maybe for comedic purposes), but for a story that you may want to target for teenage readers, it feels like a cheap way for the author to not have to go through the trouble of presenting kids like kids and not adults. That writing "cheat" becomes more obvious and annoying in that subplot of the two siblings trolling Internet forums and manipulating Earth's politics.
The ending is quite good, so it's worth going through the cringe-inducing moments of kids acting like mature adults. But then, within the last few pages, the epilogue wraps up some of the subplots in a jarring change of tone. I heard in an interview with the author that the sequel ( Speaker of the dead ) was a separate story but that by trying to adapt Ender's Game from a short story to a novel he added some subplots to tie in one plot line to the other. You can really feel that the tone and writing style is much more elevated compared to the rest of the book's "for teenagers" style, and with philosophical elements that are far more compelling. If the epilogue is of any indication of the next book, I might actually prefer it than Ender's Game.