Marcuse was the idol of the French New Left in the early sixties. By the eighties he was no long influential in North America.
From my own experience I came to the FS quite late in the mid eighties when the Lacan and Beaudrillard were the latest fashion.
I found French writing of the period to be completely hostile to rational thought and in fact nihilistic.
Not to mention both Lacan and Beadrillard were gay and Lacan died of aids. The notion that all narratives have equal value is equivalent to 'all behavior has equal value'. In the context of AIDS this is not just false but lethal.
As far as the FS is concerned I think Marxism entered its theological faze in the early fifties.
In short Marx's incorporation of Hegelian Dialectic into the notion of dialetcical materialism put an end to Marx as a serious historian and philosopher.
I think this is an important point. Marxism and the Frankfurt School aren't fashionable anymore except in very isolated corners of the academia. (For example, at UChicago we have maybe one serious Frankfurt School-type, Moishe Postone, among a sea of postmoderns.)
I want to say that the postmodern Nietzschean left is less relevant than the Marxists were because their ideology is so paralyzingly introspective to the point of incoherence; but in the end, it seems to just end up in identity politics again and again.