This is the play, not the book.
A story set in a world you don't understand, characters that live using rules that are unknown, with a conclusion that leaves you with almost nothing. Is it allegory, were we supposed to understand something about the boy and his family, who knows. You are just left with a series of visual effects that are occasionally delightful, but as they don't explain who and what these supernatural people are it ultimately has no meaning. Understanding is a prerequisite to entertainment and don't let anyone tell you otherwise. The last thing that happens in the play is a big yawn, literally.