Johnny Greenwood from Radiohead did the whole thing.
And the ending to No Country For Old Men was in a way a let down, but if you watch it again and pay attention to what Tommy Lee Jones says at the beginning of the movie it makes sense. It's supposed to be that these police men go thru their lives without ever really having to use their guns or see a triple homicide, but times change and people with it. And there comes a time when what you know doesn't fit anymore, and you need to adapt or get out.
And the original ending to There Will Be Blood was supposed to be Daniel beating Eli to death with a tumbler and then bowling his body into the pins, but they thought it was too graphic. I thought it was fine the way it was, but the other ending would've been a hundred times more badass.