I found that the words of the Greeks came back to me as I was watching The Debt Collector. "Those whom the gods will destroy, they first make mad". It seemed apt for a modern tragedy in the tradition of Sophocles.
The best technique that Neilson used was lighting. It's rare to have a movie that goes from such brightness to such gloom. The wedding scene, for instance, was as bright and cheerful as you expect such a scene to be, but after Keltie's parting shot, we are outside, in the rain, the dark, the gloom... perfect!
The violence is something that others have commented on. It is so unlike the Hollywood violence that we are accustomed to seeing. This violence is very real, and more shocking and horrifying because of it. All the male lead characters were capable of violence, and it made me wonder how close we all are from such displays.
The Debt Collector is a story of hatred gone to extremes. It spoke to me of how hatred and revenge are empty ideas... and how it is much more important, if difficult to forgive those who have harmed you, and not to live in the past.
This movie is not for everyone, but if you are interested in tragedy, then you should see this film.