Well you have to think about the band's artistic goal. Sometimes repetition is necessary to communicate certain messages. For example, I don't Filosofem could achieve what achieves without the use of repetition.
But there are also plenty of records with lots of variety, i.e. the first two Emperor Records, the first two Burzum records, A Blaze in the Northern Sky etc.
To me, Transilvanian Hunger communicates human impulse detached from human emotion. It's a totally inhumane sound. That's an abstract idea, I know, and I'm sure other people would put it differently, but I think that's in the region of why this record is so compelling to so many people. It fucks with the way we normally hear humans express themselves and in doing so depicts a very primal experience.