What a magnificent film! Fritz Lang, again a foreign, not American director is pushing social convention and using sound to get us to connect to the characters. Films are turning inwards and exploring themes and characters that were much harder to portray in the silent era. Certain storylines require the nuance of the human voice and not just facial expression to get across highly complex psychological conditions. Especially in regards to Germany, this film sits in the lexicon of foreign movies challenging the political and social conventions of the day. You see movies acting as agents of political and especially social change. The old aristocracy is being eradicated across Europe, especially with the aftermath of WW1, but now more so with the advent of mass media of films and is delivering a death blow to the ruling class.
This is truly a movie for the masses. It has both the escapist and adventurous elements of a crime thriller mixed with a highly human cast of characters who challenge the grey area between villain and protagonist. I would argue this film is a precursor to the Anti-Hero of the 1940's. You as the audience are forced to sympathize with the villain by the sheer nature of the film featuring his character right off the bat and thus you are inherently challenged as a viewer just like the townsfolk within the film to question your understanding of right and wrong as is done in the penultimate scene of Peter Lorre being put on mob trial for his actions.
One of the creepiest elements of this film is the use of sound, especially the whistling of Peter Lorre's villain. It is at first quite innocent and especially innocent when coupled with the shots of the playing children, but as soon as you see his shadow appear over a wall and understand what is going to happen to that child you feel chills down your back, mostly coming from the sound of his whistling, and then its absence. This is a trick that will be used many times over in horror films throughout the decade, providing a repeated sound that establishes a pattern and then that sound suddenly dropping out to denote something horrible is about to happen.