The fascinating thing about this movie for me was the behavior of Anton Chigurh (played by Javier Bardem) relative to other characters. Chigurh seems to be the only guy in this movie with frontal lobes, particularly in terms of his ability to model the other characters' behavior, while they're utterly at sea about his next action - like a human playing with a dog. The difference in the use of language is particularly striking: the rural hayseeds he victimized throughout the movie are uncertain, approval-seeking, making simple, naively truthful declarations. Chigurh only speaks to cause an effect - his words are noises that move things - and the effect is sometimes a certain behavior from one of the hayseeds, and sometimes to amuse himself. If he says something true, this is incidental.
What's so fascinating about this? Because although Chigurh might be the only person in the movie who has free will (as opposed to reflex and instinct), he seems not to believe in free will: he has placed his behavior, or believes it is inevitably, under the control of rules and fate. In this scene, he is (we assume) determining whether he'll kill a gas station attendant based on the flip of a coin:
The tension in this scene is among the best in the history of film. Do note the unplanned choking on the peanuts. There was no rule, no fate there, and it hurt him.
Later in the movie, when Chigurh is about to kill Woody Harrelson's character, he asks if "If the rule you followed brought you to this, of what use was the rule?" The ending is interesting in that Chigurh gets into a bloody, near-fatal car accident - accident.