Perfect film IMO. Also one of the best theater experiences I've had. Never seen a film hold an audience hostage like that. The violence was at such a level that you could tell people were on edge, to the point people let out a sigh of relief during this scene:
There was audible relief that folks didn't have to actually SEE that.
I think the ending was brilliant, and ties perfectly into the beginning. It's really summed up by the convo with the cousin:
The sheriff realizes he's no match for the world or the heights of violence/evil he's up against. In the dream where he said he lost some money he was given, it's like he acknowledges he failed. And his reward isn't to be with his father, at the end of the road/life. It's to wake up, still in this new world he cannot comprehend, and wait his time while reliving his failure and watching things get worse.