It does get rather dull: the book covers sixteen years or so, most of which are spent on horseback traveling between places named Caer Something that I could never keep straight. I liked the stuff about the horses, and how war horses differ from regular horses, and the breeding of horses, and how many horses it takes to support how many people, and so forth. If military logistics don't interest you, or horses, the book won't hold much appeal.
As a feminist version of Arthurian saga there are things I quite liked about it: the integrated military, the fight training, the farm management (just typing this makes me feel like the dullest person ever). I really liked that Sulien ap Gwien is such a prickly character, who only gets along with other people in a bluff, military sort of way. She's very good at what she does, and she's smart enough to recognize a trap, and she's smart enough to stay well away from the politics and religion and relationships that don't appeal to her.
But still, that's a hell of a long time to be slogging around a small rainy island waiting for things to happen. I'll read the next book just to see what she does with it, but I can't imagine these will ever be my favorite Walton books.