With Belus, I think you had a number of problems. For a start, Varg hadn't been in a recording studio or even touched a guitar for sixteen years. He was relearning his craft, probably working out some ideas that had been ticking over in his mind for a very long time; whether he should have released these efforts is another matter, but hey. Furthermore, Varg had (presumably) been almost completely isolated from music culture for a lot of that time; he spent a great deal of that period denouncing black metal and saying he would never play it again, remember, despite the fact that some of the interviews in which he described these views may be apocryphal; there are a number of Varg Vikernes interviews floating about that he has explicitly stated he never granted, and which contain glaring factual errors (one talks in the introduction about Vargs cell window overlooking a forest, despite him being at the time in a prison on an island in a cell which looked over the yard), and a number more which are suspect. Anyway, Belus to me smacked of a man who has been out of touch for a long time basically rehashing themes of his adolescent output, but without the vitality or relevance they had back then; after all, part of what makes Burzum such a touchstone is its huge influence on a range of traditional, atmospheric, pagan, depressive, ambient and so on black metal bands. With Fallen, it seems to me Varg is not only becoming more comfortable with the process of making music and trying out new ideas (Clean vocals!) but he also seems to be reconnecting with and listening to more music that came out whilst he was in prison. Probably not just black metal (Varg is known to have tastes that include electronica and Dead Can Dance), but there is a definite sense coming through in Fallen that Varg is now aware of developments in the folk/black/pagan/viking milieu, and is aiming towards developing an individual and distinctive voice again. There are moments of genius shining through once again on this album, I think, and memorable tracks. Jeg Faller is really nice.
What I personally think the music really needs is for the keyboard to come back, and slightly more adventurous song structuring. The keyboards could be used sparingly (I'm not quite suggesting he becomes Summoning) to provide flourishes and texture, whilst the songs could benefit from more sudden changes of direction, crescendos etc.
All in all, this album gets me excited for what the next one will sound like.
