Isengard is a one-man-band by Fenriz, formed because he had some ideas that didn't fit into Darkthrone. He wanted Darkthrone to be Darkthrone, and not become progressive. Isengard can be described as Folk Black Metal. Most of the material is inspired by Norwegian culture and old superstition. Fenriz goes out from the heathen Norway, before the Christianity was forced into the country. If you like Storm, this is the music for you. Vinterskugge and Høstmørket also includes some really Black Metal songs, like Darkthrone. But it is the Norse-inspired songs that really make Isengard so fantastic. Another thing that makes Isengard, is the demo-sound. It is real crappy production. That's because Fenriz loves lousy production.

Source : http://www.geocities.com