The genius of Ender's Game is its simplicity. The story naturally fits this style because the main character is a child. And the entire premise of the book is rooted in the observation that children show more skill at unraveling complex spacial relationships and at reacting instinctively and decisively to complex changing circumstances than mature adults. (Think of the Rubik's Cube puzzle - it took me, at age 35, fourteen hours to solve it the first time, whereas there are kids who have picked it up and solved it in minutes.) The simplicity of the theme goes beyond a child's perspective though: don't expect anything but the barest essentials of visual description or context. This is primarily a ride through a mind-scape: What it feels like to be Ender Wiggins and think like a child prodigy. More on that in a minute.
Ender's Game is dripping with intensity, but what I found most remarkable is that Card paints the tale with true believable emotion at the same time. This is pretty amazing considering it is basically what I call "Primitive Grunt Fiction" - that is, its all about self-preservation and using brute force to enforce it, the basest of animal instincts.
The story is about a kid who becomes a whiz at video games and uses that skill to remotely control a real military mission. Wonderful and believable (assuming you accept the zero-delay faster than light communication without which the entire premise breaks down). But a huge portion of the story takes place in an artificial enclosed zero-gravity "Battle Room" in which the characters use the walls and exits as key tools of their strategy. Wait a minute - space doesn't have walls. In the battle room the kids are the 'ships'. They propel themselves by intertia alone. Wait a minute - space ships have internal propulsion. Bottom line - sorry, but it's a real stretch to believe that confined "battle room" training would be the centerpiece of a training program for space warfare. Swallow hard and suspend disbelief.
Now back to the mind of a child prodigy. Card proclaims in his introduction that he never felt as though he thought like a child--and he uses this hopelessly-skewed first-person observation to justify projecting fully adult thought processes into his child character. Yes, survival instinct is fully functional at that age. But psychologists will tell you (and research confirms) that a child's ability to project the long term consequences of his/her actions is not. Some of Ender's behaviors exhibit mature, critical forethought to a level that even most adults don't achieve. For me, that destroyed the realism of the story. But once one decides to overlook this flawed premise, they can settle back for an enjoyable ride. It's one of the classics.