I may be grading on a curve, because there are so damn many "remember this, boomers?" documentaries and this one blows them away.
That's mostly because of the subject, though I've seen awful documentaries about interesting musicians. Crosby has aged from a smug asshole into a wistful, funny folk-pop elder statesman, and the archival material is superb. We don't just hear that Crosby was impossible to deal with; we see a long, cringe-inducing clip of him commandeering a CSNY media hit, buzzed and over-confident, to ramble about politics. We don't just hear about his decline, we see a montage of clips revealing just how bloated and phoned-in he became for a long stretch of the 1970s.
This very easily could have been a sloppy Behind the Music clip job, and instead it's sad and insightful and memorable.