At first I thought this was going to be some sort of combination of The Tombs of Atuan, The Name of the Rose and philosophy of science; our hero is a trainee scholar in a rigidly ritualistic academic culture which covers his entire world. But then it turns out that this is a First Contact story, and we have the build-up to a brilliantly described commando raid in deep space. And our hero resolves the problems in his love-life, so the romantic in me was satisfied too.
I particularly enjoyed Stephenson's playing with words: the honorific "Saunt" drawing on both savant and saint, the "Concent" combining the characteristics of a convent with undertones of concentration and concepts, our hero's name "Erasmas" echoing most obviously Erasmus but perhaps also Rasselas and others with similar names. There are a lot of neat and witty allusions to well-known concepts in the history and philosophy of science. Erasmas' home, the Concent of Saunt Edhar, is located at 51.3° north, the same latitude as London, or Greenwich, or indeed Bath where Herschel discovered the planet Uranus.
Stephenson loses marks on a couple of technical points, though. I mentioned last week that he has his polar orbits wrong. Also, like Asimov in The Gods Themselves, he has matter brought into universes where the nuclear forces don't operate in quite the same way, in which case I would expect the atoms to either collapse or explode, though I suppose there could be some handwaving explanation (or perhaps I've misunderstood what "newmatter" is supposed to be).
I expect it will be a tight race between Anathem and The Graveyard Book for the Hugo this year. My vote goes to Anathem.