It's hard to mark this movie because it's hard to put it into a category. It is romance, social satire and drama in the same time. This guy breaks into houses and lives inside them like they were his own, while the owners are gone, without actually stealing anything. I don't want to spoil the ending, but I think this is the main pillar of the movie, the idea that one can succeed on living in the world, but out of sight. This is a movie for the true pariah, the one that wants to be left alone, in silence, in his own world.
It is said that the best warrior wins the battles without fighting. If that's true, then Kim Ki-Duk is amongst the best dialog writers ever :) The characters say nothing, but tell a lot.
I think it is a movie worth watching, it's quiet and has some original ideas that can catch your imagination if in the right mood.