It’s a creepy, poetic freak-out that makes clever use of a subjective camera.
Essentially, the movie’s about a young couple that gets stalked by a witch in the woods. It seems to be telling a folk tale about sacrifice and love, and it tells it beautifully. Almost everything in the first half of the film is shown from someone’s POV. This slasher-film motif gives the film genuine power and suspense.