Part of why it works is by the nature of its subject, the book and its various plot points and devices serve essentially as metaphors for almost anything-- anything related to how humans communicate and remember.
It's not just superficially a fun sci-fi romp, it's also a story about the stories we tell ourselves and each other, about how we assign meaning to events, among other things. It reminds me just a very little of Godel Escher Bach, but I like this one better. I am also reminded of Lewis Carroll, and the cryptic quote that "through the looking glass is the best book on mathematics for the layman, since it is the best book on any subject for the layman"
It is poetry. It is a Rorschach blot about Rorschach blots. I can't recommend it enough.