In terms of interest, the plot is little better than decent. Also, the characters are fairly flat. Why five stars you may ask? Sheer force of ideas — in quantity and quality. Anathem exemplifies one of my favorite roles of science fiction as a genre: to play with the possible and to spur highly intelligent imagination.
This is a difficult book to review without spoilers, and I’m not going to even try. However, Though knowledge thereof is not necessary to understanding the book, I can recommend Anathem highly if you enjoy any of the following subjects: mathematics (particularly geometry and topology), quantum physics (particularly the many-worlds / world-branching hypotheses), Latin, the structure of religious orders, hierarchies of thought, philosophy, metaphysics, the sociology of religion, cycles in history, individual spirituality, and/or political intrigue.
I think it is destined to enter the canon of Great Science Fiction Novels That Any Self-Respecting Fan Should Have At Least Read.