NS Black Metal
Some, like Doom and Grind, are (mostly)useless because the style is so limiting that only a few bands are needed to sum up the genres. Most NS Black Metal is poorly done Norway and/or Graveland worship. Others, like gothenburg, viking metal, brutal death/goregrind, industrial metal and most power metal exist because the ideas in Death, Black, and heavy metal are all used up, so in place of creativity, bands just mix extreme metal with heavy metal, add some flutes to go along with horribly done "folk vocals", squeal like a pig to a poorly played blast beat, and revert back to rock n roll.
Edit - Doom refers to trad doom and not "deathdoom" like Asphyx or dISEMBOWELMENT.