This movie came pretty damn close to being a complete masterpiece. The credits are by far the best credits I've ever seen anywhere, and are more exciting than some entire movies. The cinematography, lighting, camera work and effects are some of the most original I've ever seen, and absolutely genius. The first half of the movie is tight, effective, fascinating and well-acted. But the second half is about 40 minutes too long, overindulgent, repetitive, and dull.
I could tell what the rest of the movie was going to be after about 45 minutes... this would've been fine if Gaspar NoƩ hadn't decided to then painstakingly show every last detail of it over 2 more hours. The storytelling technique used was great, but also very long in transitioning from scene to scene, which made it painful to watch when you had to sit through two transitions to see a useless 1-minute scene (which happens often in the second half). Plus, while I'm not usually one to complain about sexual themes in movies, I felt this one was completely gratuitous in being as explicit and close-up as possible, while throwing in sex scenes apparently at random. This was far from Black Swan's elegant use of shock value.
Still, the first half alone makes this not only worth watching, but a must-watch for any movie enthusiast. Who knows, maybe the second half won't bore you to death.