Are music documentaries part of this? I only ask, because I find Martin Scorcese's music documentaries (all his documentaries, in fact, maybe with the exception of italianamerican which I have never seen but looks really good) to be surprisingly glib and amateurish, the very opposite of his great works (yes, I love Mean Streets, Taxi Driver, Raging Bull, After Hours, King of Comedy and Goodfellas just like everyone else does, I'm not being contrarian).
He produced a massive multipart documentary about the blues which my father owns, and watching it with him I was amazed by its laziness and poor quality. He's apparently planning a Bill Clinton doc which sounds like it's going to be a cheap and embarrassing hagiography, as his Stones and NYRB films were.