The most obvious point of comparison for Xasthur would be Burzum, who pioneered one-man black metal, but Malefic's songs are far more grandiose and epic. He tops their shrill guitars, onslaughts of double kick drum, and demonic vocals with layers of organ and synth and what at times sounds like a choir. His aesthetic walks the line between truly evil and brilliantly beautiful, which is pretty common in contemporary black metal (consider Liturgy or Wolves in the Throne Room).
Malefic ended Xasthur in 2010, and on 10/31 he'll release the first record from his new project, Nocturnal Poisoning. No previews are available yet, but he says on his Facebook page that it isn't a black-metal record—it was made with all acoustic instruments.
Here are the two available parts of One Man Metal:
So far the documentary is excellent. The only part of it that isn't totally great is when they show Jef Whitehead, aka Wrest of Leviathan, playing one of those dorky electronic drum sets. Part three will be out soon.