I've seen it numerous times and I show it to all my metal buddies. Definitely a great documentary. Entertaining and informative, with stuff for both newcomers and diehard metalheads. Also some fucking great interviews, like the ones with Gaahl and Mayhem.
Metal Evolution was a solid series, but I felt it was sorely lacking, obviously due to network intervention. Given that the most relevant things happening in metal today are mostly in extreme metal territory, it's absolutely ridiculous to completely shaft it like that in favor of episodes on grunge and such. I'm sure they felt the same way, and I hope he can make another documentary about more extreme metal with the same production values.
His Iron Maiden tour documentary Flight 666 is great. People should totally watch that.