This is an important film because it depicts an event and an aspect of life in the extermination camps that is little-known. It is not meant to be a tear-jerker, or a film on the level of Schindler's List, especially since it does not tell the same story. What it does tell is the brutal reality of the only armed revolt staged by the Jews in Birkenau (the extermination camp attached to Auschwitz). The Sonderkommando ("Special Detail") were the prisoners that were forced to assist in the annihilation of their own people by taking the bodies from the gas chambers to the crematoria. In order to keep their crimes against humanity a secret, the SS liquidated each Sonderkommando every six weeks. This is the story of a group that stashed away weapons and explosives and revolted just before they were scheduled to be liquidated.
After having read Eyewitness Auschwitz, written by a member of the Sonderkommando, and "Auschwitz: A Doctor's Eyewitness Account" by the completely self-absorbed doctor (in reality, not the movie) upon which this film is based, I'm glad this project was undertaken. It is a well-made movie that tries to portray too many of the complicated issues that involved with the subject. It has received some harsh criticism, especially by some who claim to be interested in the subject, but obviously missed many points in the movie. Since I don't know of any other films about the revolt of the twelfth Sonderkommando of Birkenau, I think this one is very good.
One final note: Some people seem to think that the title refers to some moral dilemma faced by the characters. While that certainly was an issue for some who were there, and while the movie title may convey a double meaning, the main reason Birkenau was referred to as the Grey Zone was due to the coating of ash from burned human corpses that covered everything, including those who lived and worked there. It was on the ground, on the buildings, and on their clothing. They literally ate and breathed it 24 hours a day.
