Set back in 1930's China the story is about a treasure map. The Weird dude steals it during a train robbery. So now the Bad guy and his gang are chasing him, but there's also a Good guy who's a bounty hunter and he's chasing both. But that's not all because you also have the Japanese Army and a bunch of other secondary gangs showing up and blasting the shit out of everything.
Tons shooting, massive body count, catchy music, excellent cinematography, outstanding direction by Kim Jee-woon and the three leads are all really good. My only complaint is it's probably 20 minutes too long.