Both good looks into the world of metal, however both are missing vital pieces of information that I'm going to blame on time constraints than ignorance or an impartial viewpoint. Sam Dunn has even gone on the record saying if he could do six hours worth of material he would, and even then you would only be able to scratch the surface of metal as a whole. If you're curious about learning more about metal these are good starting points, but if you're looking for something with more of an "umph" then you're better off looking for other documentaries.
In
Metal: A Headbanger's Journey the scene with Gaahl from Gogoroth is hilarious.