Carelian Satanist Madness is an amazing album. Of Celtic Blood and Satanic Pride by Drowning The Light speaks to me in a similar way. As far as the Xasthur side of things goes I would recommend Leviathan or Striborg. If Watain is too clean then Striborg is the complete opposite. Expect potato / no-fi recording quality but the atmosphere is everything. Ascetic Meditation of Death by Cult of Fire is getting near daily listens from me recently, Witchrist and Vassafor are also quite often listened to many times a week. Spire is doing a great job of reminding me of the Darkspace / Paysage D'Hiver binge I went on a while ago. Cauldron by Ruins is a great album and is always in my playlist, but I'm starting to prefer Front the Final Foes... Temple Nightside have a kind of Portal vibe and Impetuous Ritual have some of the Portal members in the band. Here are some random bands that I think are great too; Nazxul, Vrag (Australia not Hungary), Behexen, Von, The Amenta, Silencer, Pestilential Shadows