I haven't seen it for a while. but one thing that stood out for me while watching it, was that it was audacious storytelling -- not on the part of the Coens, but on the part of Cormac McCarthy -- to kill off the main character long before the story is over.
I haven't read the book, so I don't know how it plays out on paper. But in a movie, it's a weird thing to do, because it could easily leave the viewer feeling suddenly rootless. We follow Josh Brolin's character and his struggle, expect the story to be his journey, and it suddenly isn't anymore.
Plus, he's killed off-screen, another odd move. Again, it yanks the rug out from under the viewer.
I'm still not sure exactly how I feel about these factors; I can say I liked the movie, but these moments of character and and narrative disorientation alienated me from it somewhat. Perhaps others felt this disorientation to be exactly what made the movie great for them.
In any case, it's not my favorite Coen Brothers film; that would be "Miller's Crossing." I really enjoyed "True Grit," and thought "A Serious Man" was the most thoughtful, mature film they've ever made.