It's generally agreed that director Fritz Lang made his best films during his early years in Germany. These are the ones that are constantly revived and revered, and rightly so.
But the greater part of the director's career was spent in America where, between 1937 and 1956, he made 22 films (as opposed to 13 during the German years). This latter period is seen as a rather dreary coda to his halcyon days, with only a few films grudgingly granted a certain distinction. But the fact is that many of the American films compare favorably with the German ones, though they are more modest masterworks, made in an admittedly less glittering mode.
Part of the reason for the primacy of the German films in the Lang canon can be explained by the simple fact that they remain landmarks in the history of world cinema --visually striking, original, influential. Dr. Mabuse, The Gambler (1922-23), a film in two parts and running nearly three-and-a-half hours, was the prototype of the modern spy movie as well as the gangster epic. It was also the first fully realized rendering of the Langian theme of pervasive evil, a malignancy both supernatural and ruthlessly efficient, represented by the director's mingling of irrational, shadowy expressionism and those psychologically acute, pictorial compositions that signaled modernity.
Metropolis (1927) was an extravagantly envisioned capitalist dystopia, although the horror of masses of workers being turned into literal cogs inside the mills of industry was somewhat obscured by the attractive geometry of their subjugation and the machinations of Brigitte Helm's quaintly seductive android-vamp (a silly film, was H.G. Wells' considered opinion). It remains Lang's most popular movie, many of its comic book (sorry, graphic novel) aspects still being recycled.
The high point of the German period was M (1931), Lang's first talkie and next-to-last film before leaving the country for (briefly) France, then America. This is one no one would dare dismiss as silly. Its complex sympathy for a child killer still cuts deep, its director's blend of shadow and sharp angle still seems contemporary.
So, first of all, the American films have to be measured against these, though it helps to keep in mind that the works from the two periods were made under very different conditions. In Germany, Lang was a big fish in a smallish pond, exercising as much autocratic control over his films as he possibly could. In Hollywood, he arrived as a relatively obscure figure and one not temperamentally suited for the studio systems -- he fought his bosses from the start and lost most every battle. Even more important, in terms of sealing his reputation stateside as a diminished master, he made genre films -- crime melodramas, noirs, even a few westerns.
There's a reverse chauvinism at work here -- who wants to assert that a homegrown potato like the relentlessly grim Edward G. Robinson vehicle Scarlet Street (1945) is as fine a film as that imported bit of caviar, M? But it is, and its story of a kindly, mild-mannered painter who becomes a savage murderer is vintage Lang, its depiction of slowly encroaching, world-shattering evil directed with the same archly observant precision as in the earlier film.
Because of the conditions under which they were made, Lang's American films are less flamboyant than his German ones, but they also have an added ingredient missing in the earlier movies -- a sense of normalcy. Although Hollywood strictures prevented him from making any nihilistic epics a la Mabuse, they also insured that the films would be grounded in a quotidian reality, making the intrusion of moral chaos even more devastating. Lang's films got smaller, but they also became more poisonous.
In Fury (1937), an average Joe -- played by that most average of average Joes, Spencer Tracy -- is making his merry way cross-country when he's arrested for a crime he didn't commit. Once imprisoned, he's besieged by a lynch mob which sets fire to the jailhouse. Tracy survives the blaze, but only after having been turned into one of those sad and horrible Langian monsters.
In The Big Heat (1953), Glenn Ford's decent cop is no match for the forces represented by Lee Marvin's psycho-thug, and so must go through hell before reaching the necessary "happy" ending.
There are other American Langs that one can recommend without hesitation -- The Woman in the Window (1944), Clash by Night (1952), Beyond a Reasonable Doubt (1956) -- and more than a few about which one would have to concede that even a strong directorial personality couldn't salvage them. But if the six mentioned here were viewed by the same discerning audience that relishes M and Metropolis, then the general perception of Lang might change -- from one of a European master who was chewed up by the Hollywood machine to that of an enduring artist who made important contributions to American cinema.