Tense, well acted. Reminds me a bit of some of Polanski's films as far as his use of paranoia, his method of playing with reality versus hallucination and the way he builds tension (The Tenant, Rosemary's Baby, Repulsion).
Almost experimental. Great soundtrack. Moody as hell. Tracking shots like those of Birth. Reminds me of Roeg's "The Man Who Fell to Earth" in that the film is experienced through the eyes of the alien. Not much is explained. I like the mystery.