There are definitely some bad documentaries. The Anvil documentary is NOT good. Pretty much just about these two fuckheads and how they want to be rock stars, and them complaining about how they're not rock stars. It doesn't really seem like they have any particular dedication to the music. It's engaging enough that it feels pretty moving when they finally take the stage in Japan, but ultimately it's just fluff. The recent Get Thrashed documentary was also not very good. There's really nothing very interesting, it just covers the same shit everyone already knows. Metallica vs. Megadeth, that crap. On a side note, I've noticed that Scott Ian is in absolutely every documentary on metal. I feel like the man does nothing but interviews. He seems to be trying to become a spokesperson for metal. I really wish he wouldn't, because he's a moron from a shitty band.