Heart Blackened is one of those rare Korean movies out there with wonderful acting, the characters were well versed by the actors.
As the story starts, the plot seems to make sense but goes on to be more confusing. This movie might be a little hard for people who can't tolerate slow movies, but things speed up at the second half. The acting is super awesome.
Each character in the movie has a meaning which only some get, a rewatch is required to really understand the dark plot . The movie is not a hard brain exercise, because twists are to hard to predict, what at some point my feel like the end of the movie, is really isn't. What characters you make like will become what you hate at the end and also vice-versa.
Though the same message can be conveyed in a shorter time, the long ride isn't that much of a pain when you have lots off free time in your hand.
So, sit back and leave the rest to the Korea's top of the range actors.