This is the third book in a now completed trilogy. Two things:
First: I don't think that this really needed to be a trilogy, although I do think that the story needed more than one book. It probably could have been done as a duology. No one seems to write those, though, and I don't know why.
Second: Nonetheless, as you can see, I gave this a very high rating. This series hits a lot of my personal buttons, and I found the ending deeply satisfying.
I love the way that Marillier writes her romantic subplots. She is not a romance novelist, but her fantasies do generally have romantic themes. She is not one for insta-love, and her protagonists have to work at it to find happiness. I thought that the romance between Neryn and Flint was lovely.
I really did enjoy the world-building as well. Alban is an agrarian society, loosely Celtic in nature, with a more Scottish feel than the world of Sevenwaters. I loved the Good Folk, in their myriad of forms and guises. Some were recognizable to me: selkies and brollachan. Many were unnamed, but still familiar. While Marillier is no GRRM, characters to whom I was attached died in the rebellion.
I liked the ending. It was sad, yet still hopeful, happy, but serious. Very satisfying.