His first two albums, Det Frysende Nordarriket and the selftitled one are not that monotone.
They have a somehow insane, but also living, pulsating, healthy and natural feeling to them.
Also, they are more unique and not so tremolo-darkthrone-esque.
I especially like the selftitled. Nordarriket is too fragmented and one actually had to judge the single demos on the cd.
Forest Poetry and especially Strength and Anger are his most monotonous albums.
If you want to give Ildjarn's bm stuff another chance you might purchase "Ildjarn is dead" (old demos and stuff you can only get for 70€ as originals are on that album - just the selftitled and nordarriket era), or the 1992-1995 compilation, which makes a nice "mix" of his styles.
Landscapes and the Hardangervidda albums are ambient.
I don't know Landscapes, but Hardangervidda is really great and i don't think Vinterriket can be compared to it.