FURY is also an amazingly good movie and quite an unsettling one to boot. But "M" is chilling ( sort of an early NOIR, before there was such a category )and Peter Lorre at his best/scariest/most haunted.
Have you ever seen "SCARLET STREET"? TCM is showing it in December and if you haven't seen it, you should.
Remind me about Scarlett Street. Yes, M definitely has a noir flavor. Brilliant Germany before it crashed and burned thanks to Hitler. I’m also a fan of Louise Brooks’ German films, Pandora’s Box & Diary of a Lost Girl. Sexuality and sensuality without all the disgusting crap that goes on in modern Hollywood trash-fests. (Although these movies push the envelope.)