This is the best metal film I've ever watched. It's factually very accurate (the Slipknot inclusion is annoying, but the interview was good and made good sense in the film) and the music selections are perfect for when they appear. It actually covers a lot of the underground metal scene, like death metal and black metal, while having enough mainstream perspectives to remain commercially valid. We've all heard the PMRC story, but this movie covers it without getting boring by using a great interview with Dee Snider and old footage from his speech.
This is the best film, no, best WAY to introduce someone to the genre. I highly recommend it.