what makes a french comedy one of the greatest films of all time?

First shown in 1939, Jean Renoir’s “The Rules of the Game” so often makes lists of the greatest films of all time that its ranking is also potentially difficult to explain. This French film doesn’t shake up conventions of cinematic storytelling as radically as “Citizen Kane” did in 1941, nor does it have the obsessive lure that makes “Vertigo” so endlessly rewatchable. Although part of the Renoir film’s reputation rests on its use of deep focus and long takes, it didn’t invent either technique — and camerawork alone isn’t why it endures.
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But “The Rules of the Game” is among the most perfectly balanced of films: a movie about discretion that is in every way a model of it. The opening credits call it a “dramatic fantasy,” but it is not simply drama, farce or tragedy. It is a comedy of manners (even though the introductory text expressly disavows that description) in which manners act as a scrim. Etiquette and pageantry excuse the characters from dealing honestly with matters of the heart, and perhaps even blind them to the encroaching darkness of World War II.

Here.