Christopher van der Meyden’s review published on Letterboxd :
Even giants like Hitchcock have to stand on other giants. Fritz Lang is without a doubt one true pioneer of the art of movie making. Compared to "Metropolis", "M" is a completely different movie. Without any gigantism, it explores the soul of humans and of the city. Despite being 85 years old, it depicts (sadly) Germany in 2016 perfectly. A mob of angry people ("besorgte Bürger") seeks out to find the one abnormal person who threatens their honorable business, mainly being criminal. The Mafiosi would be PEGIDA and the child murderer Islamists or else. I don't dare to criticize this movie.
On the technical side, the use of audio was mastered by Lang. It was a tool, not smokes and mirrors. Lang would be maybe master 3D also on the first try, I am sure!
I just can bow before this giant on which every movie maker afterward stood.