Every bit as great as Schindler's List and The Pianist

...albeit in a different way.
Schindler's List had a moral core. It managed to find the glimmers of humanity in an unfathomably dark situation. This is what made it so moving, and what made its ending so cathartic.
The Pianist was first and foremost a chronicle of survival. It was not as moving as SL -- it didn't involve redemption, and its main character always remained somewhat remote and did not seem to change in any profound way -- but it was no less great.
The Grey Zone was the least moving of all. Clinical and detached in its examination of one of the darkest periods in history, it defied any attempts to try and find a trace of light or humanity. An ambiguous, almost nonexistent, moral core combined with an almost documentary-like portrayal of the day-to-day functions of the Nazi killing machine made for difficult and depressing viewing. But even so, it was no less great than the other two.