I watch A LOT of music documentaries. That's kinda my thing. Most of them follow the same basic formula as a longer 'Behind The Music': band starts, band gets famous, band goes through some turmoil, band breaks up, band makes triumphant return. The details change, but that's the gist complete with an ending that makes us all feel good when it's over.
This on the other hand is unlike any music doc I've ever watched.
Ginger Baker is a complete fucking asshole with no redeeming personal qualities whatsoever. If he wasn't such an extraordinary drummer I have my doubts anyone would want anything to do with him, and by all accounts most of the musicians he's worked with in the past no longer do.
Not saying it was a bad film, but don't go into it expecting to have any of the myths of Ginger debunked. He's probably a worse person than you thought he was already.