I disagree. When it comes to comedy, there was an ongoing tradition of very witty films that go from the 50s/60s all the way to the 80s, often with the same writers. There is a continuity from "le cave se rebiffe" (61) to "faut pas prendre les enfants du bon dieu pour des canards sauvages" (69) to "laisse aller c'est une valse" (71) to "buffet froid" (79) to "la chèvre" (81) or "les compères" (84)... These films are flawless, and their style is not extremely different - not to mention the same actors played the same way in many of them (Gabin, Ventura, Blier). Frankly, I don't see much of a difference of quality between "Cent mille dollars au soleil" (64) and "les morfalous" (84).

When it comes to serious movies, there was also a continuity of quality, with political or socail thrillers by Tavernier, Verneuil. Chabrol, Costa Gavras, etc. I actually find it difficult to identify the epoch of some of these movies, from the 70s to the 80s ("le secret", "i comme icare", "Z", etc), because their tones and qualities are very similar. The same despaired paranoia runs through them. The style evolves seamlessly. Would you say that "le cercle rouge" (70) is a pale shadow of the 50s ? Or that Pierre Granier-Deferre's movies plummeted in quality from the 60s to the 80s ?

The only thing that was lost, in my opinion, was the sheer poetic impact of films written by the likes of Prévert, Carné, Jeanson. This is a style and a tone that was lost (possibly killed by colours, even). It's like a dead genre. Still, when Jaoui and Bacri write a movie (or, technically, adapt one of their theatrical plays, but whatever), I take it to the guts with the same strength as an "Hôtel du Nord". And their "cuisine et dépendances" is from the early 90s. I admit they are a bit exceptionnal. But the guy who made "L'année dernière à Marienbad" in 61 made "Mon oncle d'Amérique" in 1980, and "Smoking/Non-smoking" and "On connaît la chanson" in the 90s.

I am fond of the 80s cinema mostly because of its specific easy-going action adventures comedies and thrillers, there was the 70s carelessness allied with icreased technical means. Things started taking themselves too seriously in the 90s, and started to feel too planned, to thought-of. I see the 90s was the start of the collapse towards post-modernism : self-awareness in a pretentious way, stuck between the daring not-giving-a-shit era ("Phantasm", "Buckaroo Banzai") and the self-irony and self-subversion that would follow. The 80s was the follow-up of the 70s liberation, with a tad more professionalism. Just enough to still feel sincere. I think that the 80s were the swan's song of the XXth century.

But these points may hold mostly for hollywoodian productions. What I'm getting at, it that I don't think you should oppose these decades that much, especially in french cinema. I agree that something has been lost during or after the 80s (a freedom of creativity when it comes to film productions : Tavernier was very vocal about how the production system of today would have made his own classic films impossible to produce nowadays). I'm very doubtful about a french golden age situated around the 50s/60s. There's marvels from that era, there are others from the following decades, and quite often in the exact same genre.