If this movie could be summarized in one sentence, it would be "hurt people hurt people." The movie is really good at keeping you on your toes, second-guessing what will happen next, since the character who first seems like the antagonist, is the one who actually ends up being a normal person, with their own set of struggles and affairs. As a matter of fact, each character presented has their own story to tell, whether you agree with their choices or not. The movie was also an interesting insight into Japanese culture and thought, presenting both the positives and negatives of being an orderly, but somewhat restrictive society.
In short, if you're interested in Japanese way of life or are looking for a compelling three-dimensional drama, you should definitely give this movie a try.