Satanism was a major factor in the creation of this genre and so most lyrics are rife with anti Christian messages.
Atmosphere is important in black metal, specifically a grim, cold and evil atmosphere. If hate could be condensed into a form of music, black metal would be it.
There are two main types of BM:
a) Traditional- Raw and primitive come to mind when trying to describe the sound of traditional BM. No instruments other than guitars and drums are used. Vocals a barrage of screams and rasps (listen to Funeral Fog by Mayhem). Recording quality is usually purposefully crude and fuzzy. This is referred to as the 'necro' sound.
b) Modern- Often employing classical instruments like violins as well as keyboards and synthesizers. Clean vocals (male and female) are often used to supplement the usual raspy vocals. Recording here is usually clean as is normal with most metal. Many purists hate modern black metal with a passion.
The keyboards are used to create ominous and 'evil' soundscapes. Organs and strange techno sounds are popular.
CHILDREN OF BODOM
While many consider CoB technically a Black/Power hybrid, I have put them in this section because of the vocals. CoB are now starting to get popular in North America. They hail from Finland and are very young guys. Their music is fast black metal complete with harshly-screamed vocals, but they have the wild and almost 'happy' sounding guitar solos of Power metal. A great band to get power metal fans interested in Black metal.
I think their two newest releases are the best (though many would argue). They are:
Follow the Reaper and Hate Crew Deathroll.
EMPEROR
Legends among black-metallers, Emperor is often considered one of the greatest black metal bands. However, they received tons of flack from black metal 'purists' who disdain the use of keyboards and symphonic elements. Those people are morons in my opinion, because Emperor rocks. The music is so heavy you will be beaten and battered just by listening to it. Sadly, Emperor has broken up so we shall not hear any new albums from them. Their last release: Prometheus: The Discipline of Fire & Demise is pure heavy goodness.
ARCTURUS
Before they turned to Avant-Garde metal, Arcturus played excellent symphonic black metal. They have some of the most beautiful lyrics ever. To Thou Who Dwellest in the Night is a moving piece of poetry even without the music!
EXTOL
A Christian progressive black metal band! Didn't think you'd ever see that, now did you?
Well, I didn't anyway. However, I'm glad they do exist! Extol are EXTREMELY talented. Their guitarwork makes me want to throw up it's so difficult. I love the crazy time changes and heavily distorted guitar here.
The ultimate EXTOL is Undeceived. Their newest one, Synergy, is almost as good, but not quite.
BAL SAGOTH
With a name like Bal Sagoth, one might expect ultra-evil Satanic metal. Actually, what we have here is symphonic black metal with cheesy lyrics and narration about epic fantasy battles and the like. Very similar to Rhapsody in that aspect. (A good thing in my opinion). I was lucky to find a used copy of the album The Power Cosmic for only $12.