So, to begin. Juliet Marillier is an author who is an auto-buy for me. If she writes it, I will read it. This is a longstanding position, since I initially read Daughter of the Forest about five years ago. FWIW, Daughter of the Forest remains one of my favorite books.
Marillier has a very distinctive style. Her books are fantasy, but they take place in a dreamy, historical past that relies heavily on Celtic myth. Her Shadowfell series takes place in a mythologized version of Scotland. Her writing is lyrical and gorgeous.
I particularly admire the way that she writes her female characters. She does not fall into stereotypical tropes - her women are neither one-dimensional warrior women with breasts, nor are they helpless damsels in distress. They possess varying levels of emotional or physical strength, but are always resilient and resourceful.
Raven Flight is the center book in the trilogy, and concerns the fight to overthrow a cruel monarch who abuses his subjects. Neryn, the main characters, is a "Caller" - a young woman with the power to "call" the Good Folk (roughly equivalent to the fae or fairies, but not Tinkerbell-ish fairies). The Good Folk in Shadowfell are closely connected to natural world, and are led by the four guardians, one each for the Northern, Southern, Eastern and Western Good Folk. Each compass point has it's own strengths and it's own orientation.
Flint is mostly absent in this book, as this is really Neryn's story. The brief time that he is present in the book, though, is sweet. There is definitely a Lord of the Rings feel to this trilogy to me, if Tolkien had put a greater focus (or any focus at all) on one of his female characters. I read a review that likened Flint to Aragorn, and I can see this comparison, although Aragorn is a far more idealized character than Flint.
Raven Flight ends with a huge event, and the fate of the rebellion against the evil king really hangs in the balance. Characters must step up and accept leadership positions, and acknowledge their human feelings, and it is painfully emotional. I can't wait for the third book.