Filosofem is the most accessible album, regarded as the album which could have taken Burzum to a new level of popularity (something in itself which is the opposite of what second wave Norsk Black Metal is about) had Vikernes not been stuck in jail.
Belus is a fantastic record, but it is not new material. This taints it's standing against the previous works in the catalogue, I think many people are overlooking that. However, to contradict myself, no (metal) work of Burzum has ever contained "current" material. The compositions have come from various points in Burzum's history. One could almost say each release has been a compilation if you take this into consideration.
Belus is not a consistent work. HLTO and DSEV were definitely consistent, as was Aske. Excluding Aske though, HLTO and DSEV are much more fully realised releases than Belus is.
The NEXT Burzum album is the one which will need proper assessment. Not Belus.