As far as I'm concerned, these are the ten metal albums everyone should hear, in chronological order:
Black Sabbath - Sabbath Bloody Sabbath
Judas Priest - Sad Wings of Destiny
Iron Maiden - Powerslave
Metallica - Ride the Lightning
Slayer - South of Heaven
Pantera - Cowboys From Hell
Overkill - Horrorscope
Kyuss - Welcome to Sky Valley
Vader - De Profundis
Down - NOLA
I know there's not even a sniff of black metal in there, but I think if you've heard those albums, you've heard the best that metal has to offer.
I love inside jokes, I'd love to be a part of one some day.