What I love about the good books in this series is what they have to say about books and how reading them can take you places and show you things that you might otherwise never get to see. And that's never been as well done as in this book (of the ones I've read yet, at least).
From the prologue where it's made clear that the treehouse could take them places in the books, very clearly drawing a parallel with imagination, to the books that guide them and the books that "rescue" them, I've not yet encountered a children's book that makes it so clear the magic that books contain.
Especially brilliant in this one is the contrast between Jack, Annie, and the other Librarians who are working so hard to preserve books and the knowledge and stories they contain and the book-burning Dragon King. Equally brilliant was the way the scholar-in-disguise called our time where all children go to school to learn how to read a paradise. In our culture, books and reading are taken so much for granted, and I LOVED the reminders here of how fortunate we are. I especially adored that these reminders never came across as condescending or pedantic, even though aimed at very young children.
Any celebration of books and reading deserves praise, and one this well done deserves 5 stars.