The Decline of Western Civilization: Part II is one of the most must-see documentaries in metal culture. (Hot tip: we recorded a watch-along commentary podcast about it). Penelope Spheeris, the director, really managed to get into the psyche of some of these people.
She was hired in 1999 to do a documentary on Ozzfest 1999 – the one that featured Black Sabbath's first retirement tour. The doc had the working title of Decline of Western Civilization: Part IV – We Sold Our Souls for Rock ’n Roll, but was never actually released save for some premieres at festivals including Sundance. Now, a decent-but-not-great bootleg of the entire doc has surfaced online and you should probably watch it before it gets taken down.
Besides Black Sabbath, other bands featured include Slayer, System of a Down, Fear Factory, and Static-X.
Also, read our column looking at where the bands on Ozzfest 1999 are now.