Basically I'm looking for more albums in the vein of Abigor's Nachthymnen. Maybe not necessarily the same sound, per-se, but something with songs that have a lot of different parts, which demands full attention to be absorbed, and doesn't just fade into the background like most black metal does.
Recent Deathspell Omega and Negura Bunget would also fit the bill, but I'd prefer something a bit more melodic [in the conventional sense].

Akroma. Not really similar to either one of the three bands mentioned (well, maybe Abigor), but still very varied (almost proggy), demanding black metal. They have some very melodic parts, what with violins and some female vocals here and there, but are still very intense. The vocals, specially.

Akroma, named after MTG lol.

Ok, I would suggest Agalloch, not really as black metal as DsO and Negura, but still very dynamic and good. Ne Obliviscaris is another one that would do well.

I think your best bet though would be Fen or Cobalt's Gin. Both are very varied in composition.

Kerbenok's O might also work, although that is just a straight up weird album.

That is actually a really hard request. When I decided to respond I figured it would not be so challenging. Good thread.

Kathaarsys are highly recommended, particularly Portrait of Wind and Sorrow. Audible bass, great clean and harsh vocals, lots of melody and interchangeable sections that contrast one another well. Criminally underrated.

Direwolf technical black metal - almost speaks for itself!

Apotheosis. Maltese black metal? If you say so! Widely varied band that incorporates thrash and symphonic music. Great bass, once again, keys-guitar combo that remind me slightly of the old Arcturus sound.

Might not be precisely what you're after, but it is what was first to mind in terms of complex black metal.

Quite interested in anything that may satisfy the original request. Nachthymnen is an album I hold in quite high regard.
Going through somewhat of a music rut at the moment so I'm having a difficult time thinking of something to contribute.
Maybe look to their countrymen Estatic Fear The instrumentation is quite varied, though the pacing is much slower and the compositions easier to comprehend. Very pleasant melodies throughout.

I'll second Apotheosis as well.

Abyssos, a black metal band with alot of melodeath/black influences. Great band, great riffing and changes, and some cool solos!

I also second Ne Obliviscaris.

Bloodrain.