One of the main things that I enjoy about Korean cinema is that with most of them we start the movie out with very little knowledge of what is coming up and the films tend to not progress in the Hollywood style of knowing almost exactly what is going to happen based solely upon who the star of the film is.
A Bittersweet Life actually kind of violates this "policy" in that it progresses precisely the way that we would imagine a movie with the Rock in it would yet it still manages to be very very good.
This film is directed by Kim Jee-woon who is one of my favorite directors in Korean cinema (he did "I saw the Devil" and "A Tale of two Sisters") and he doesn't disappoint in this film as he uses the same style that people like me found so appealing in his other films. It is difficult for me to describe his style so I'll just call it "excellent", I'll save the details for a film student.
A Bittersweet Life focuses on Kim Sun-woo (Lee Byung-hun, who some may recognize from his role in the GI-Joe movies) and he is an enforcer for a mob boss known as Kang. Kang instructs Kim Sun-woo to watch after his new, very young, mistress; because Kang believes she is cheating on him. If Kim Sun-woo discovers that she is cheating, he is to "take care of it."
Kim Sun-woo is a very dedicated employee for Kang and is almost Impeccably devoted to him but after meeting the girl he is meant to be watching he is drawn in by her innocence and perhaps feels sympathy for her.
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Although it isn't explicitly stated in the movie, I got the feeling that Kim felt as though his employer shouldn't have the right to claim her as he wants to. Kim doesn't appear to be falling in love with her, but he lets her and her real lover get away clean telling them he wont kill anyone if they never see each other again.
This "betrayal" information gets back to Kang and of course he doesn't like it. He decides to extract his revenge on Kim Sun-woo in a very Mel Gibson's "Payback" type fashion - but without the humor.
The way that this movie progresses is captivating from start to finish to the point where I smoked indoors because I didn't want to pause it (I never do this) and the soundtrack is chosen just wonderfully. The actors all do their roles perfectly and Lee Byung-hun is just incredible in the starring role. If you haven't taken my advice up to this point you really should start watching Korean action / thriller movies. Because this one, like the others, is amongst the best of the genre ever made (IMO, of course)