Tactician said:A big theme in the movie is class divide and upward mobility. The job market is brutal in Korea and just a few years ago the minimum wage was like $5. Competition bleeds into a lot of areas of people's lives. People look down on each other based on physical attractiveness, intelligence, and of course money/status; credit card debt is a big problem there because of the effort put into keeping up appearances. The movie touches on these themes in a layered way without being preachy.
Another heavily-layered Korean film about class distinctions is "Burning," which was discussed previously in this thread. I heavily recommend it.
The Korean cinema is great.