As Elvin said, that's almost impossible to answer. A lot depends on the mood I'm in at the time of watching. Right now I'm inclined to say The Big Lebowski.
Other possibilities: Fargo, Heat, Fear & Loathing in Las Vegas, Amores Perros, Donnie Darko, Usual Suspects, Godfather 2, ...
I've heard it was based off a book but not much more than that. I like the idea of a post apocalyptic background and Viggo Mortensen is a great actor so I hope it isn't mediocre