This is simply an excellent crime/drug movie with great acting and great cinematography. If you are an individual in the younger generation (teens, 20's, 30's) you will most probably enjoy this movie. You get a very stylish look into the life of the Pusan (second largest Korean city; also largest port in Korea) drug/crime underworld.
In fact, Busan is famous for it's gangsters, being the second largest city of Korea and also a mecca for import/export trading. It is also the closest point between Korea and Japan. After the war (WWII), a lot of Koreans and Japanese inter-migrated through this city, during a time when industrialism and yaks gangs developed tremendously.
Knowing this, you may get a better understanding of the scenery and setting of this awesome movie.