Going back to "Carnal Knowledge" and "Bob and Carol and Ted and Alice" mainstream film after the demise of the studio system has explored sexual morays pretty thoroughly and even though Alan Ball wrote a script that was his own sardonic, irreverant view of American life it is not all that original. The dialogue is incredibly well written as it is in "Six Feet Under" (and by multiple writers other than Ball) and the story had a new twist on looking at homosexuality among other themes. Alternative Cinema has to by definition be other than a commercial Hollywood product, an independent film. Although Miramax finances movies, for instance, are perhaps efforts which the big studios like Paramount or Universal would reject does not necessarily make it "alternative cinema."
Here's one definition:
http://www.hi-beam.net/fl-defs.html
Sam Mendes who directed the movie from the Alan Ball screenplay has a good track record, "Road to Perdition" being his last offering and he is going to bring Sondheim's "Sweeney Todd" to the screen (although there is a video of the stage production, in fact two). I don't think you can take the name actors out of the mix as that belies the film being alternative cinema. All these classifications are, of course, subjective. There are several sites on the Internet if one searches Google and none of the films come close to being anything like "American Beauty."