Angelina Jolie's new film on the Khmer Rouge is impeccably made, but will it get under your skin?

How do you depict a nightmare? How do you re-create — and do justice to — events completely outside ordinary human experience?

Filmmakers who represent the Holocaust have dealt with this dilemma for decades, and Angelina Jolie faces it in "First They Killed My Father," her examination of the nightmarish...