Somewhat mysteriously this book is widely considered by science-fiction fans to be the best work of science fiction in the last 30 or 40 years. The book has a number of flaws, the most important of which is denied by the author in the introduction. The book is a portrait of gifted children and goes into depth into their psychology, it however completely fails to capture the psychology of a child, even a gifted one. Ender is 6 when the book begins and while at times his psychology may be that of say a gifted 12 year old, it never remotely resembles a small child's. They just do not think that way. In fact, this goes to the primary flaw of much genre SF these days. There has been an ever greater emphasis in SF on character and psychology, but this has gone hand in hand with a very real lack of insight into the human condition. That has meant that SF has gone on to be less and less readable and is in my opinion a genre in decline. The book has large elements of nerd power-fantasy to it that I think have been missed by the book's author and fans. It is more objectionable than the nerd power-fantasy of the 20's and 30's in that it is claiming to say something profound and it just is not, whereas the traditional stuff sometimes accidentally would.
That being said the book does have some merits. It is highly readable and reminds me of a less excessive Heinlein. It is really quite good in it's space opera elements. Worth reading, but really worth reading as light entertainment and nothing more profound. There are a few interesting ideas about guilt and power, but not so much about children.