I might not be the right person to answer, as I´ve always had a strained relationship with black metal and it´s only in recent years I´ve come to appreciate select artists in the genre, but I have a good friend, who is big black metal fan and who has played all sorts of artists for me over the years, and even dragged me to a couple of black metal concerts too (I´ve seen Satyricon, Dimmu Borgir and Mayhem twice). So I guess I´m sort of qualified to discuss this subject.
One of the things my friend has always loved about black metal, at least the eighties/early nineties artists, is the focus on individuality and nihilism. A bleak worldview where only the strongest survive. But that´s of course only part of what black metal is about. There is a wide field of other themes covered by other artists, that doesn´t focus on those things. Take for example the whole viking black metal movement, spearheaded by Enslaved. That´s a whole other ball game. There are even a couple of Christian black metal bands out there in Horde and Drottnar (which I might add is a killer band). There are also the absurd/avant garde type black metal acts like Dødheimsgaard and Ved Buens Ende.
