Probably more like 3.5 stars, objectively, but I can't really give it a rating that says "really liked it" when... well.
I liked it well enough, I suppose - enough to read until the end anyway. But while all the right ingredients were there, and it should have been exciting and terrifying and imaginative (and was, at times, to an extent), I never really connected with either the characters or the tale itself, and it's hard to be truly excited by a book when I don't actually care much whether someone lives or dies.
I did like the idea of Briar - it's not often we get adventure books with close to middle-aged (old enough to have a teenage son) women as the protagonists, and not the usual jaded but hot urban fantasy heroines at that. And I by and large liked Briar herself, too; I just didn't really come to care.