Reincarnatedwolfgod said:
Aside: Just quoting because I took about 15min to write this and I think it's not a bad "Intro to Metal" tutorial (if I do say so myself).
OT: You have to ease yourself into it. Start of with heavy metal, then move up in the following order until you find stuff you like. Below is a list of subgenres that provide a decent understanding of metal, ranked in order of how heavy they are. Included are some examples and their best albums.
Punk Rock & Post-hardcore (not metal but a good starting point for aggressive guitar)
Rise Against (The Sufferer and the Witness)
Experimental
Apocalyptica (Inquisition Symphony; 7th Symphony)
Van Canto (I don't know any of their albums, this one's just good for a laugh)
Heavy Metal
Iron Maiden (Number of the Beast)
AC/DC (Back in Black)
Black Sabbath (Master of Reality)
Thrash Metal
Metallica (The Black Album; Master of Puppets)
Megadeath (Risk: Japanese Edition {comes with Duke Nukem Theme})
Nu-metal & Power Metal & Symphonic Metal
Nu-metal Examples: Avenged Sevenfold (Avenged Sevenfold; The City of Evil)
Power Metal Example: Kamelot (The Fourth Legacy)
Symphonic Metal Example: Epica (Design Your Universe)
Metalcore
Trivium (Ascendancy; In Waves)
All That Remains (The Fall of Ideals)
As I Lay Dying (An Ocean Between Us)
Deathcore
Suicide Silence (The Black Crown)
Death Metal
I don't know any death metal...