I admit to not being entirely rational about the Sevenwaters Trilogy. I first read these books as a teenager and they resonated with me such that I read them all many times. While I'm not sure I would give this book five stars if I came to it with fresh eyes today, I do so anyway because a) an author who can inspire these kinds of feelings in me is doing something very well and b) this book is certainly on par with the first two in the trilogy and does not deserve its lower Goodreads rating.
While it's helpful to read the other two books first, Child of the Prophecy can work as a standalone: a generation passes in between and there's a new heroine, a young sorceress named Fainne (pronounced Fawn-ya). She's the daughter of Ciaran and Niamh from the previous book, making her the granddaughter of Oonagh, the sorceress out to destroy the Sevenwaters family. The plot of the book revolves around Oonagh's blackmailing and manipulating Fainne in an attempt to destroy her family.
Many fans of the previous books seem to dislike this one for reasons that aren't flaws in my eyes: it's rather bleak in tone, the heroine is far from perfect and the ending is bittersweet. In other words, if you're just looking for a light romantic read, this isn't your book (in fact, the romance is a much more minor element here than in the previous two). Fainne is a difficult character--she does some terrible things, and with her isolated childhood and present secrets, she has a hard time bonding with people. But to me this makes her interesting: she has serious inner conflicts, and sometimes she makes the wrong choices. It's also fascinating to see characters and settings we came to love in previous books from a different perspective: many of the "good" characters dislike or mistrust Fainne, and she feels the same way about their beloved forest.
The book has a gripping (although not fast-paced) plot, engaging characters and a lyrical prose style. Inner turmoil and growth, which are prominent, are well-done and balanced out with dialogue and a bit of action. Magical elements, while obviously strong given the heroine's abilities, are well-done, fitting into the setting and retaining a sense of wonder. It's not perfect--in particular, I'd note that the heroine is often far too perceptive for someone who has spent very little time around people in her life, and that there's perhaps too much talk at the climax. But I can't imagine a better conclusion for this trilogy: thematically and in terms of plot and character, Child of the Prophecy works excellently.