personally, I think metal lyrics are awesome. even the caveman style like Beherit or Immortal. I love that they use the same symbols and phrases over and over. there's something Zen-like about the repetition.
I've always thought poets should stick to the traditional symbols like sun, moon, night, day, rivers, mountains, eagles, lions. In other words, the exact opposite of comparing the sunrise to an etherized patient on a table.
I don't think there are any metal lyrics that have the strength to stand by themselves without the music, though.
it would be important for Metal Literature to not be TOO literal in its translation from the tradition of the music and its lyrics.
off the top of my head, the most metal piece of literature would have to be Blake's Marriage of Heaven and Hell or maybe even the Book or Revelations.