I didn't realize that this movie was NC-17 before I saw it, but this is one of the few films that I think legitimately deserves the rating. It's adult. Not because it has lots of nudity, not even because of the gore, really, but because there are some pretty dark, twisted, and messed up segments. I'm somewhat sensitive to scenes of cruelty/humiliation and it was just this side of tolerable for me at times.* That said - I really, really enjoyed it. It reminded me of Fargo and No Country for Old Men. Black humor, violence that teeters between cartoonish and horrifying, gorgeous landscapes, quirky characters and best of all, plenty of good old fashioned storytelling. It's a wonderful thing, the way cinema can occasionally capture the simple art of a lone individual spinning a good yarn.
Astonishingly, everyone in the movie manages to be sympathetic and interesting despite being arguably rather vile. What is even more impressive, they are quirky yet believable, recognizable types without being cliches. The acting is wonderful, the dialogue is a delight, and it's a fantastic, atmospheric film. Much recommended.
*I think its important to warn people of that before they see it (I was not warned about the Girl With the Dragon Tattoo, and I walked out of the theatre, and resented everyone who had recommended it to me without mentioning how brutal it was).