Although Viking Metal and, more general, everything connected to Black/Extreme/whatever Metal isn't really my cup of tea, I really enjoy Vintersorg from time to time... just his newer, spaced-out stuff, of course.
I'd recommend "The Focusing Blur", which features a lot of absolutely crazy tracks next to "The Thesis's Season". It's REALLY exhausting, though, at least for my ears... not only due to its bleak heaviness, more because's there so freakin' much going on! String sets, black-ish chainsaw riffs, organ swells, electronic loops and effects, hectic percussion (by Asgeir Mickelson), jazzy bass (by Steve DiGiorgio!)...whew!