I'm actually a big fan of that Nokturnal Mortum album, hahaha. I might just be a subhuman, but I really dig their first four albums, which show an interesting transition from keyboard-heavy neoclassical/folky Emperoresque black metal to Graveland-inspired pagan positivism. Haven't gotten around to hearing their 2009 album yet, though. The de-emphasizing of the guitars is really more due to production restraints (the inability of low-budget studios to handle two keyboard melodies, two guitar melodies, and an often independent bass melody vying for space at the same time) than any real failing on Nokturnal Mortum's part. If you fuck with your EQ settings or the stereo balance a bit, you can hear dramatically different interpretations, similar to what you can do with the second Deicide album.
I'd say that the bands that have taken the "symphonic" black metal idea the farthest are either ones like Abigor
and Obtained Enslavement
who use the "symphonics" to dramatically deepen the level of counterpoint and melodic layering in their music (a bit hard to pick out with low-bitrate YouTube samples, unfortunately), or bands like Summoning
who leave the realm of heavy metal-based music entirely in favor of making neoclassical ambient soundtracks with black metal aesthetics. The vastly underrated Parnassus
from Sweden might be seen as straddling the two styles. Dub Buk
have their own weird take on symphonic black metal in that they play percussively rhythmic black/thrash that utilizes occasional but regular bursts of symphonic stuff in order to transition between riff-sets and keep their songs narratively interesting. Mörk Gryning
uses symphonic black metal tropes in a similar fashion on their debut album, bringing more depth and variety to the too often overly saccharine style of Dissection/Unanimated/Sacramentum/Dawn-esque "melodic" Swedish black metal.
Basically, I think that symphonic black metal is a cool idea, but it's been given a bad name by the likes of Dimmu Borgir, Cradle of Filth, Mystic Circle, and even more respectable names like Limbonic Art (good sense of the epic, but often overly repetitive), Mactätus (occasionally well-written, but often hit and miss when they try to ape more mainstream-accessible stuff in the vein of the third Dimmu Borgir album), and later Emperor (high on dramatic pretense, low on transcendental content).