There is really very little you can criticize about a story when the story is true. The adaptation for the screen can come under scrutiny, but in this case there really is no cause for concern. It is a beautifully shot and crafted piece of cinema. Excellent Cast, and solid direction.
You are introduced to a view of history from a less common angle. The lives and story of people who opposed the rise of Nazi Germany from within. People who stood up to the fear, collusion, and general despair of the masses. Most too scared to fight back, choosing instead to lay low and hope for the best.
You can draw frightening parallels with the world today. Except we have social media to voice our anger and concerns at what we see as injustice. The tyrants and demigods around the world fight to block free speech on the internet just as Hitler and the SS did in Germany in the late 1930's and 40's. If you disagree with them you are wrong and risk being silenced and oppressed.
This film depicts the pre-internet world's attempt at quiet resistance. Slower, less reach, but still shows the importance of non conformity in the face of oppression. A valuable watch for all who love true stories, and perhaps particularly relevant at the moment.