I suppose I should clarify the intent of this thread: I'd like to start a general metal discussion and music sharing thread - for all genres of metal.
To start: I will explain a brief history of the genre. This may come as a surprise for some (not judging) but metal traces its roots in Classical and Blues music. Early Heavy Metal musicians (Blue Cheer, Deep Purple, Cream, Rainbow) fused the complex song structures found in Classical music with the attention to personal musicianship, musical exploration, and expression of Blues music. This, combined with the stage performances and attitudes made popular by Punk and Rock music, is what defined early Metal.
This continued for some time and, as more and more bands picked up the styles and experimented with sounds, the genre progressed and branches formed. The first most notable sub-genre of metal is called Thrash Metal. Early Thrash acts include: Metallica, Slayer, Exodus, Over Kill, Anthrax, Testament, Death Angel, Destruction, Venom, Kreator (there are tons more).
Thrash Metal fused the ideals of Metal musicianship with the speed and intensity of newly emergent Hardcore Punk. Also, notable is the highly sarcastic and 'punkish' nature of the bands' images. Metallica is largely credited with creating and popularising the genre.
Then enter bands Death and Possessed: the commonly cited creators of what became known as Death Metal. This genre of metal is mostly characterised by very intense styles of playing, a focus on playing faster and more technical, with markedly much more experimentation than Thrash (basically means that Death Metal musicians are a little more sober and focused than early Thrash Metal). The most obvious characteristic is the 'death growl': a style of singing which I am having a particularly difficult time describing with words alone (ironic as I'm a vocalist myself) so, check out Cannibal Corpse, Death, Bolt Thrower or Malevolent Creation for some pretty obvious examples of the style. (You can't miss it)
Enter the 90's. Here, some would argue that metal began some kind of decline in quality, really a lot of popular bands began experimenting and Grunge and pop began to overshadow Metal (which was very, very popular worldwide at the time). More importantly, this is the decade in which 'Second Wave' Black Metal began its rise to infamy (and some great music). Øystein Aarseth, otherwise known as Euronymous is usually credited with creating the Black Metal sound; this actually has some truth to it: Euronymous did popularise the characteristic tremolo guitar playing of the Black Metal genre. However, I prefer to focus on the objective, larger picture. Celtic Frost (a Swiss band from the mid-eighties) created a style of songwriting that focuses on creating atmosphere with less focus on expert musicianship or complex song structures (basically, they didn't care so much about showing off - never mind that they probably couldn't). This music became very popular in the 'metal underground' and another band - Bathory - is the one that I, personally, credit with the Black Metal sound (seriously, check out Under The Sign of The Black Mark). Anyway, Black Metal focuses on songwriting and atmosphere. Its sound is very distinct: tremolo guitars, blast beat drumming, shrieked vocals, and very terrible (I like to say 'raw') production quality. This is arguably the most difficult style of Metal to acquire a taste for but, I promise, there is some great music here (yeah, it's my favourite).
There's tons more but there's the basics.
I'm tired of typing about it so enough of that squidward. Talk about what you're into.