I don't think that was it. Every scene individually was great. Really good cinematography, high end crisp performances especially by Brad Pitt imo. But as a whole I didn't see where it was going, apart from the aging actor having to face the fact his best days are behind him and the golden age of cinema is changing around him (as is America as well e.g. the hippies, Polanski etc).
I get it a bit more now with the whole Manson stuff though.
Funny thing is, I wouldn't actually disagree it's a superb film

but mainly because as I said every scene individually was top drawer. At no point did I want to stop watching. Go figure!