To me In The Nightside Eclipse is the Nespithe of black metal, it just doesn't sound like anything else out there. I get what you mean that it's hard to get into, but for some reason both ITNE and Nespithe clicked with me the first times I heard them, maybe because both just sound completely natural.
The first time I heard ITNE I count as one of the best musical moments of my life, I was in a cabin in the middle of nowhere, lying in bed and looking through a window into the sky, and the music just fit perfectly. An example to symbolize just exactly what I like so much about the album (more people should do like this and not be so sweeping all the time); in Cosmic Keys To My Creations & Times, at 2:32, to me the music is "sighing". It's full of things like that that I can't really explain how I like them. It's the same with Nesphite, so incredibly otherworldly.