As recently observed in an article in 'The Atlantic', metal (and even 'brutal' metal like Deicide) shares with New Age music an interest in the trascendant. Readers of the DLA will of course already appreciate this.
However it is a mute point to observe that styles of metal which aren't traditional black or death are concerned with trascendence. Bands like OM, Sunn O))), Drudhk (as described by the article) all evoke meditative, reflective, 'spritual' atmospheres. I do not happen to enjoy OM and Drudhk (I like Sunn O)))), and I think that they do not share the same compositional techniques as old school black and death metal, but nevertheless they, like psychedelic bands, some forms of electronic music etc, are obviously motivated by some sort of desire to get beyond the individualistic and solipsistic themes of rock, pop, rap, R&B etc.
The unique compsotional structure of old school death and black metal I think seperates bands belonging to these genres from bands ike Drudhk and OM, and also perhaps the themes of death and black metal bands puts them a rung up the ladder, literally. It could be argued that although stoner, doom, drone, psychedelic music is concerned with the transcendent in appearance, beneath the surface it's really just escapist psychology. You get high to reverb-laced guitars, and lyrics about ancient temples etc. However, the same argument could be made of death and black metal. Even though the themes are more 'realist' (war, death, combat) than doom, drone, stoner etc (and leaving aside the issue of its compositional uniqueness), you can cite countless examples of fans of this music being completely introverted, detached individuals who are hiding away in their medieval fantasy worlds and avoiding the battles they should be engaged in today, here and now in the real world. It is a fine line.
Taking a different direction: even if death and black metal do evoke a different variation of the quasi-transcendent themes of a wider variety of music (more 'war-like' or 'ascetic'), the factors which elevate metal, comparatively, then become purely political ones. 'Music X is more transcendent than Music Y because it takes approach 'a' to issues of war, nation and other people as opposed to approach 'b'. This is political and so the issue hinges on one's conception of what exactly transcedence is (is it the path of action or contemplation, for instance? is it an aristocacy of the spirit, or is it universal compassion? etc)
The most objective factor seperating old school black and death metal from other quasi-transcendent music, then, is its compsitional structure. http://www.theatlantic.com/entertainment/archive/2012/08/doom-metal-has-a-dirty-soothing-secret-its-a-lot-like-new-age-music/260582/