Tim Blake Nelson, the director of "The Grey Zone" (USA 2001), states that this is not a movie about the Holocaust. It is about the choices a human being is ready to make in order to stay alive - even if it is just for a little while longer.
The central figure is Dr. Miklos Nyiszli, a Hungarian Jew who assisted with Josef Mengele's infamous experiments. The events are based on his records and on notes of members of the "Sonderkommandos". They take place in Auschwitz, 1944.
The SS dropped the Zyklon B into the gas chambers - everything else was done by Jewish prisoners: leading the victims into the changing rooms, assuring them they were going to have a shower, locking them in.
Then, afterwards, collecting the bodies and burning them in the crematoria ovens.
There was even leisure time for them to play chess or to enjoy the items they were able to loot.
And the question for the viewer becomes: how would you have chosen?
The impact of this film results from it's coolness, it's unsentimentality. It is much worse than "Schindler's list" or "The Pianist". Those were stories of survivors.
The movie was shot in Bulgaria and the extras were recruited from the region. They were queuing up for roles women had to shave their heads for and people lying naked on top of each other as "human lettuce" in the gas chamber (information from the bonus material).
If you want to learn about the death camps in the third Reich - watch the BBC series on Auschwitz. If you want to understand more - watch this.