Tricky to get the subject matter right because the worst excesses of Glam are so over the top. I've seen much better documentaries but it has some great points. It's strongest feature are the creative people associated to the cast of characters from the world of music. If a documentary gets this right and gets them talking in an interesting manner it's always doable. You can make a documentary about anything no matter how cheesy.
Lot's of working class boys from the Midlands in this one (shout out to Slade). Bryan Ferry drips style and there's a momentary glimpse of David Bowie at Marc Bolam's funeral getting into a chaffeur driven limousine and looking flawless.
Sombre but perfectly flawless.