Great for children (some sections are lovely for adults as well), I though the tone of writing was really precious (in keeping with the tone Lewis himself had when addressing his younger audience in the Chronicles - of endearment and recognisant of children's potential and value).
The book is full of pictures: beautifully illustrated by Pauline Baynes, the illustrator chosen by Lewis to do the whole Narnia series (there are some new illustrations made specially for this book) and there are also photos relevant to Lewis's life and pictures done by C.S. Lewis himself when he was a boy.
There is a biographical section adapted for children, a section on what inspired Narnia with glimpses in the writing process (I was hooked), a summary section with timelines and maps, a section on geography, one on characters, a little section about its hidden meaning (I was disappointed of the shortness of this section as I have expected that most of the meat of the book will be here) and a last short section on the appeal of Narnia which touches a little on the end of Lewis's life, on the impact in the books (its adaptations for example), and - I really loved this part - it encourages children to try their hand at writing, too.