They're not a post-rock band. There is definitely some post-rock in their sound. Lots of building up and calming down, lots of climaxes, very epic, very poignant. There is also a very traditional folk sound, despite not using much "traditional instrumentation" (mainly cuz they're American and it'd be weird to use Scandinavian instruments or whatever to play folk). There is some black metal, but not enough to call them black metal at all; they are not minimalistic or raw, nor do they use tremolo riffs to a great extent. I'd say there's a fair bit of doom in there as well, but I would not call them doom either, as they lack the spirit of doom found in many bands (generally exceedingly slow tempos and love of all things doomy). They're kind of a mutt.