- (Earlier) Black Metal was characterised by deliberate lo-fi production quality on recordings (see the Emperor-Enslaved split for an example, also early Immortal, Burzum and Darkthrone).
- Black Metal vocals tend to be a high shriek, as opposed to the more "harnessed" sound of lower growled death metal style. If you found Grutle's vocals on Frost tough, listen to Varg's vocals on early Burzum! LOL. It takes time to get used to, but once you do, there is an appreciation you can get from it. I actually find it quite cool now.
- the repetitive drumming is known as blastbeats. It takes it's influence from punk (as Black Metal does overall anyway ie the musical style is influenced by punk). The master of blastbeats is Trym from Emperor, that man can blastbeat faster than anyone else!
Blastbeats can be pretty funny actually - when I first got into Black Metal (now my favourite genre, mostly second generation BM), I found blastbeats hilarious and it was hard for me not to burst into laughter. Mind you, some Black Metal bands are just too awful and deserve a good laugh!
Immortal took blastbeats are turned them into something really interesting though: see the "Damned In Black" and "Sons of Northern Darkness" albums. Blastbeats in short bursts sound really brutal and powerful, I think they're more effective this way. On the other hand, the latter Emperor records had amazing blastbeats in them, but the constant presence of them went well with Ishahn's symphonic ideas (see his work on Peccatum as well).
In summary - Black Metal isn't as easy to digest, certainly took me a while, but once you can appreciate it, you'll be amazed at some of the bands who have extended the Black Metal foundations and branched out further (see [later] Borknagar, Solefald, Peccatum, Arcturus, Naglfar, Negura Bunget).
I really feel that later generation Black Metal is where all the growth and experimentation is right now, there's some really exciting stuff going on.
Hope this info is handy