I find it strange that we now have so many documentaries on Norwegian black metal, and yet none of them deals with the actual music at any major depth. That being said, it was nice to watch Varg debunk the basis for all the media-created sensationalism that has come to surround this movement. Oh, and Hellhammer proved himself to be an even larger idiot than Frost.
I think Until the Light Takes Us does better than focusing on the music in depth, it focuses on the impetus behind it. If you want to learn about the music on it's own there are plenty of resources for that already, namely the music itself.
From my two viewings of this movie, I would say "focuses
on the impetus" behind the music is a strong term. It's split between impetus from Varg's side, hypocrisy by Fenriz, relation of scene-related events from everyone and a rough investigation of each actor's personality and how this relates to the music. Certainly, the aim was never to give a detailed analysis of the music in terms of its composition, genealogy, and so forth, but there's some skirting around some issues, and I don't even think it's intentional.
As for what would improve it: more interviews from other key scene members, as well as deeper exploration of isses Varg addressed, but Ferniz seemed not to (whether he was questioned on them or not is anyone's guess), with key members and tying the threads together. Examples: How is Varg's killing of Euronymous related to his disdain with the scene at the time, if at all? Was it a case of Varg viewing Euronymous as a "weak" leader, or a clash of personalities leading to a (pre-meditated) self-defense situation? Bit of both? How does Fenriz's apparent disdain with "modern black metal" link up with his feelings about society in general, and the phenomenon of cultural "dumbing down" or "selling out"? Or is he just a music-/modern-art-man? What justification does he give for his more "provocative", newer material, because "makes you want to kill yourself" is emo, not provocative in any sense, and, how does this link up with his stance on most of the new, "modern black metal"? Is he not a part of the very thing he claims to dislike? And so forth. Note: I haven't seen any extra footage (besides Hellhammer talking about "Death Breath"), so my opinion may be severely misinformed.
So, I would say, from my understanding, it seems that the directors, perhaps inevitably, sought to find an impetus for the music and the extreme actions related to the black metal scene by investigating the personalities of some
key members. This is a reliable method as any, but the thing is: personalities change over time, and I believe the personalities of Varg, and especially of Fenriz, essentially the progenitors of the norwegian black metal scene from the perspective of this documentary, have changed to the point where an incomplete representation of norwegian black metal is given. Perhaps probing deeper on certain issues, and emphasizing how this affected the music and scene at the time, may reveal more of what the situation (music, people and actions) was like at the time. Of course, this approach may just degenerate into the current muscial/political/philosophical opions of the scene members.
That being said however, I think the documentary goes much further than others I have seen in exploring black metal beyond the "satanist music" filter, and actually puts the church-burnings in some sort of context, for instance. Varg's ideas on Christianity, Norwegian culture and society in general are also telling of his motivation for, not only his music, but his world-view really. But again I feel this could have been expanded (though further claims of Varg-worship may have been made about the movie).
Maybe it needs another play (if I have to hear Bjarne Melgaard say "I think Frost is like a dark aaaangel" again though, I might puke).