De Mysteriis Dom Sathanas was released at a very "good time", considering all the free promotion it got due to the Grishnack/Euronymous things going on. This record turned a lot of people into fans of extreme music. "A Blaze In The Northern Sky", the Emperor/Enslaved split and Burzum's debut CD never received such promotion, and were classics just in the underground. DMDS was the closest black metal got to a "mainstream" record at that time. De Mysteriis Dom Sathanas is a brilliant record. Simplistic, with "weird" vocals (I actually love Atilla's vocal performance) but also with killer riffs. The most important aspect is probably the atmosphere they managed to create with this record. Brilliant stuff.
Paddok mentioned the "waves" in black metal. The first wave of black metal mainly was from 1991 to 1994. Important records are Darkthrone's "A Blaze In The Northern Sky" and "Under A Funeral Moon", Emperor's "Wrath Of The Tyrant", Enslaved's split with Emperor ("Hordanes Land"), Satyricon's "Dark Medieval Times", Immortal's "Pure Holocaust" and Burzum's "Burzum" and "Aske". These records are the essence of the first wave of Norwegian black metal.
The second wave consisted of bands like Gehenna, Limbonic Art, Borknagar, Arcturus (their debut album) and Dimmu Borgir.
A lot of bands were started, a lot of these bands were boring rip-offs of the abovementioned bands. Symphonic black metal became more popular, and some would claim that the "raw" black metal was slowly dying out. I wouldn't agree with a statement like that. There are several raw black metal bands out there; Taake, 1349, Ragnarok and Tsjuder are a few examples. Instead of following the tried and tested "raw" black metal formula, several bands are creating music I'd call "post-black". There are lots of interesting bands doing this: Borknagar, Arcturus, Solefald. Black metal had to progress, you can't just continue doing what Darkthrone did in 1994.
I just listened to Graveworm's latest album. I was shocked when I heard a cover of the terrible REM song "Losing My Religion". THAT is moving away from black metal's ideals. A lot of bands are still carrying the black metal banner high, though. Black metal is not dead, although some bands are moving into a too mainstreamy direction.