They used to be doom metal, but have recently changed styles (in their latest two albums). I think wikipedia classifies them as "alternative metal" or "atmospheric metal." In any case, they're pretty much amazing. Personally, the only downfall I would see to having them headline a night is that you might get an entire crowd just going to see them and not really caring about any of the other bands attending. Them alone would probably sell out a show (but who knows, is that really so bad?). I would love to see them in concert and I know a good deal of my friends would too.