This is a successful novel and easy to read: the story is interesting, and I started to care about some of the characters. I don't read a lot of books set in this period, so the setting reminds me most of the human-inhabited parts of Middle Earth. The broad outline of the plot reminds me in a general way of Foundation and Empire, though I'm not suggesting any close resemblance.
The book is mainly about pre-gunpowder fighting and warfare, which will appeal to some but not to others. Unusually for such a story in such a period, female characters are quite strongly represented, which is welcome in a way, although the Ladies of the Order (nuns as horse archers?) strike me as a bit implausible. Was there ever such an Order in our own history, I wonder?
The abbreviated way of speaking used by some characters is mostly OK but sometimes not readily comprehensible. I'm a fast reader, so if I have difficulty I'm afraid I just skip it and go on with the story.
I can reveal that David Friedman is a softie: despite the many dangers of the story, he doesn't kill off any character you might care about. This is somewhat implausible, but will come as a relief to any other softies out there (such as me).
Our hero Harald is repeatedly and seriously wounded, but shrugs it all off and comes up smiling after a suitable period for recovery. Considering that he's a grandfather, I boggle a bit at this; evidently a very tough grandfather.
I've long wanted a novel that would bring to life the kind of (modern) society envisaged in Friedman's much earlier non-fiction book, The Machinery of Freedom. Obviously, Harald is not this kind of a book; however, now that he's demonstrated the ability to write fiction successfully, there may be further novels...