Anathem takes place on a world not unlike our own called Arbre, where science is a sort of religion, and there has been a longstanding conflict between scientists and laypeople. The scientists have retreated to monasteries called concents, and they only interact with the outside world at certain intervals (every year, decade, century, or millennium, depending on their level). They’ve also been forced to renounce most technology, so the “avout” intellectuals spend all of their time on abstract and theoretical inquiries rather than applications. At the novel’s beginning, the narrator, Fraa Erasmus, is in his late teens and tasked with personal dilemmas like his choice of order (which are divided around the aforementioned philosophical questions), but he soon becomes involved in a situation with global implications.
It’s hard to say much more about the novel without spoilers. The plot doesn’t get going until over 300 pages in, and there are facets of the world itself that are major reveals fairly late in the book. I will say that we’re told early that the titular “anathem” is a ceremony in which avout are expelled into the “saeculur” world, so it’s fairly obvious that these two worlds will eventually collide.
I think Stephenson is probably the most exciting sf writer out there right now, and this novel does deliver big ideas and (eventually) an exhilarating story. The world building contains some nice ideas, and the monasteries are well-developed with their own politics and mysteries (and, hey, since they’re monks, they have to have cool martial arts as well!) Stephenson spends a lot of time inventing etymologies for new words. “Anathem” for instance, merges “anthem” and “anathema.” Sometimes it’s entertaining; sometimes it can feel a bit precious and self-indulgent (and, are we supposed to assume that the novel’s language, Orthic, is identical to modern English?). Also, the world’s history is very similar to Earth’s. This is largely intentional, but some of the similarities go too far. Thelenes, this world’s Socrates, makes all of the same discoveries, and uses the same techniques, and apparently lives the same life. Again, I can imagine arguments for why this might be, but it's mostly because Stephenson wanted to talk about Socrates in the context of this world. In other words, he skips some great opportunities for some Rice and Salt-esque alternate-history-building.
It’s also, like Stephenson’s last novel, too long. I, for one, enjoy Stephenson’s long digressions. He’s quite good at making a lecture into something that can illuminate the plot, world, or characters at the same time it gives you something to think about. In this novel, however, the lectures seem to be far more repetitive than usual. Almost every one has the exact same point, which thus gets hammered into the ground (I hope I never see the phrase Hylaean Theoric World again). I preferred the more eclectic tangents of his previous works. Anathem does feel like a chore sometimes. If three or four hundred pages had been cut, this would have been a much stronger work.
These complaints aside, it’s an exciting novel that really pays off in the last few hundred pages. Each act is more exciting than the last, and the climax is fantastic. I’d have to say it would have been my Hugo pick. I’d certainly recommend The Graveyard Book to more people, and it does seem like a more polished, and finished work, but I think the ambition and scope of Anathem more fully realizes the promise of speculative fiction.