This is the story of Jess, a poor boy whose going to middle school, and Leslie a new girl in Jesse’s class. Fortunately, they live very close and they start a friendship creating a new fantastical and whimsical world called Terabithia.
The book is well-written, in particular for a younger audience, with a focus on the characters and on their relationship as friends: it is very weird how the movie adaptation made it more about the fantastic world and not about the beautiful friendships Jess and Leslie had. It’s amazing how it was highlighted how a world invented by the mind of two child can mean so much for both of them.
In the end, it is a sad story and about the character grieving. It's amazing how the writer was able to describe pain in such a ‘younger’ but at the same time realistic way: the feelings of the character whose grieving are real and the reader can feel the pain.
The characters are amazingly portrayed, in particular Jess with his interior thoughts being the narrator. His mind is of a 12 years old but still relatable to more adult audiences. I also really liked the characterization of May Bell, Jess’ younger sister, and, of course, Leslie.
It didn't have a full rating of 5 stars because some things were problematic but I want to preface that this book was published in 1996. Of course, at that time, most themes that now are normal in book were taboo but there are important themes that are just put in the story and never elaborate. An example is physical abuse that is just mentioned for one of the minor characters but it isn't well described and it seems just as something 'normal'. 
I also understand that the book is from a child point of view, so it’s probable that the theme really didn’t interest him so were not described. Nevertheless, was a pity.
In general, I really recommend this book, in particular to young children or adolescences.