I liked it more than Enna Burning but less than the other two books in the series. As other reviewers have pointed out, Rin is a difficult character to get into. This is necessary, given that Rin herself doesn't know who she wants to be, but it also means that I was bored by the book until about halfway through.
As with all the books in this series, Forest Born features a heroine struggling with some internal flaw or failing, and Rin's was an interesting one: she knows that she has the power to do evil things, and she hates and fears that part of herself. For me, this was one of the more ambitious character arcs that Hale has tackled, but it's such a . . . I don't know, a large idea, that it's easy for it to overwhelm the story and make it tedious, in the same way that Enna's fire addiction did in Enna Burning. But I think in general this book works better than Enna Burning did. The first half is under constant threat of being overwhelmed by scenes of Rin sitting around feeling confused and full of self-loathing, but it pulls itself out of that mire eventually and lets Rin grow. And it is a really interesting issue to give Rin--I think a lot of us have certain aspects of our character that we dislike and try to hide because we're sure that if other people knew about it, they'd stop liking us.
In general, a pretty good book. The reason this book gets three stars instead of four is that in the final act, there is a part that just frustrates me terribly. The villain, who is a known liar and manipulator, gives our heroes a piece of bad news with no concrete evidence, and they all believe her unquestioningly. I mean, I know she's a good liar, but really, not one single person questions it?