You should check:
in Slaughterin Natives
it is "apocalyptic" dark Ambhient (or something like that)
I use 4 of their albums: Enter Now the world, Resurrection, Sacrosancts Bleed and Purgate my Stains.

I allso use lot of Funeral Doom Metal bands.
It really is good depressive music for this game....
few bands:
1000 Funerals, Funeral, Noembers Doom, Runemagick, Painful Memories and the Funeral Orcestra

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