Comic Book Confidential is one of the best documentaries on comics and has a timeless feel about it. Made in 1989, it remains relevant over time. Generally, it's a historical rather than a 'confidential' look at the medium. But it is so well executed that one has to admire Mann's witty, creative and heartfelt approach. I've seen a few other documentaries on the subject and few 'feel' as personal.
However, as this IS a vast subject, Ron does run out of time, leaving one begging for a sequel. We see snippets of the late Jack Kirby, and you find yourself wanting to see more of the man. Ditto for the other creators.
The documentary leans heavily towards the underground and more adult aspect of comics rather than the men-in-tights superhero genre so be prepared. If you're expecting to see an extensive in-depth explication of Batman, this is not the documentary to watch. If you want an overview of American comic book culture and a peek into its varied nuances, Comic Book Confidential is for you.