Yeah, it's a Coen best.
Spoilers
The movie is about the illusion of security. It is not nihilistic, but rather, paints a universe of cosmic indifference, one where luck is both good (finding 2 million dollars) and bad (getting shot in the throat for helping someone). However, it is also a world where the strength of your moral conviction plays directly into your fate, a Coen trademark. Note what happens to a character because he decides to succumb to the wiles of a strange woman--note the fate of Bardem's character, a sociopath who lives stringently by his own warped morality. But mostly, as in Jones's eloquently delivered bookending monologues about dreams and reflection, it is a movie about the illusion of security. The safety of marriage with a strong man, the safety of a corporate office, the safety of the desolation of the desert, and, most notably, the safety of a green light.
This is a movie about the sheriff. It's about the weight of headline tragedies. It's about seeing horror after horror, day after day, telegraphed in the headlines. It's about the way we shake our heads, confused, trying to make sense of the random chaos of the world that we're so distant from. The way the third act felt was a stroke of genius. We don't see a major character's death, nor is there any tension, nor is it tied fatefully to the thriller aspects of the plot. It's random, confusing, and absolutely brilliant in the way it shifts the film into perspective.
From incredibly tense thrills to a shocking sadness, but not a melodramatic one, as in Before the Devil Knows You're Dead, No Country for Old Men is genre alchemy of pure cinematic grace. The sustained frisson in the first half's experiments with aural tension and tight framing, while still capturing the same mood of phenomenal atmospheric hugeness that Mann toyed with in Miami Vice, is some of the best filmmaking I've ever seen period. It only becomes more unexpected in pleasurable, sad, and resounding ways. Technically, it's all tip-top, direction, editing, cinematography, etc. The whole cast is excellent, particularly Bardem who I feared was gonna be a one-note character, but instead turned out to be pretty much the fiercest, most unpredictable psychopath I've seen in a movie. Rather than employing him as a "force of nature", as one character puts it, the Coens and Bardem give him a disturbingly wet-eyed humanness (note the extended sequences where he's shown treating his own wounds), which ties the film's rebuke of hollow motions of amoral genre tropes (note one character's response to the idea that Anton is "the ultimate badass").
I think the complaint about its lack of dramatic conclusiveness, while an understandable disappointment, misses the greater rewards its ending is offering. If it was executed in a more traditional way, its themes of the weight of indifferent cruelty would be lost in all the conventional melodrama.
This is a special movie that I am convinced is the most considerate and momentous picture the Coens have made.