"It’s been years since I’ve read Patrick McGilligan’s Fritz Lang: The Nature of the Beast, but if I recall correctly, toward the end of his life, Lang was coming around to the conclusion that M would be the best film he ever made. If so, I certainly wouldn’t argue with the man. If he were making films today, Lang would probably be known as something of a geek. An artsy geek, maybe, but one with, besides a remarkable sense of composition, a penchant for state-of-the-art technology, its possibilities and implications. Which makes the use of silence in his first talkie all the more impressive. The other major asset M’s got, of course, is Peter Lorre."
Source