I saw it and would consider myself a Metallica fan, but a waning one. (perhaps my tastes grew a bit) I found much of it interesting, but little more than a super Behind the Music. It was interesting to see a more in-depth showing of the dynamics within the band. Also most interesting were the scenes with Dave Mustane.
However, by the end of the film I found myself annoyed at the perpetual whining of each band member. To be honest, I feel that my previous view of the band and their *manly* partying ways, though based in ignorance was more favorable than now knowing about their "struggles" and their "feelings."
This film is for devout Metallica fans. This film is not for metal fans in general. Metallica, in my mind, will forever be clouded with an association to whining wankers.
For what it's worth....
edit: grammer