Black metal, for many, is an intensely personal music, that would fail to thrive in the public sphere. I can certainly relate to that, given that i almost always listen to black metal with headphones, usually just before i go to sleep. Some might argue this explains my disturbed sleep, and oddly violent and visceral dreams, but i think that's just looking for excuses.
Anyway, i do think that black metal is a deeply private affair, containing meaning only you can probably explain. There is nothing inherently interesting, on face value, about a bunch of dudes in kiss paint, writing structureless songs. But its depth and subtlety as a genre, result in it being much more than the sum of its parts.
Black metal creates worlds in a way no other music does. Hardcore tends to create scenes, where people congregate to share ideas and values. Thrash does a similar thing. Black metal, on the other hand, projects an image of both the natural world, and the the world of humans. I think this, now that i think about it, is what i find so appealing about it. Only the listener can respond to that world, and how it appears to oneself, hence the private nature of the music.
When i listen to Burzum, or Wolves in the Throne Room, the experience created isn't one to be shared, because it delves into a part of my mind where sentiment, rather than language is in control. I can't express, really, how this music makes me feel, other than to to point to that particular emotion and state that it makes me feel thus and thus.
I suppose it's a little like the fantasy worlds that are conjured by certain childhood books. Kids read them obsessively, cover to cover, so entranced are they by the worlds they are projecting themselves into. And, when the book finally ends, there is a distinct sense of melancholy that they have to re-join the normal world.
In the same way does black metal create worlds, for me at least, and it is with the same sadness that i rejoin the real world at the end of an album. Varg from Burzum has often said that black metal is supposed to create a trance like state for the lsitener, a sentiment which is echoed by many other musicians, notably Aaron Weaver from Wolves in the Throne Room, who states that the only real logical response to the music is to fall to one's knees and weep.
The world you are transported to through black metal is a lonely and cold one, where Nature might have prevailed over the Enlightenment values of rationality and science of the past four hundred years. The sadness you feel, when listening, then, is a sense of deepest nostalgia for a time that has long passed - one that we will never be part of.
That's probably a good thing though. The middle ages were pretty fucking unpleasant from what i hear.