I actually just picked up the remastered versions of the first three Sabbath records, and, god-damn, these are heavy as f*ck!
Try to imagine hearing this for the first time in early 1970. The only TRULY heavy music yet available was the first two Zeppelin records. Deep Purple's "In RocK" was released later in 1970.
So, you drop the stylus on the debut, side 1, and you instantly hear the rainfall, the thunder, the eerie church-bells, then.....BOOM, the music begins. It's chilling! Lyrics dealing with darkness.....name ANY band that was this dark back in the day!
Sure, Zep & Purple had their dark moments, but never to this effect.
Then, after losing that 'dark edge' on the "Never Say Die" record, they completelly reinvent themselves with the awesome RJDio & release one of the genre's FINEST moments, "Heaven & Hell"!
In my view, the "heaviest records" ever released (based on the time they were first unleashed):
Led Zep I, Jan 1969
Led Zep II, fall 1969
SABBATH & PARANOID, both 1970
Deep Purple, In Rock, 1970
Judas Priest, Sad Wings 1976
Rainbow Rising 1976
Mercyful Fate, Melissa, 1983 (more for the vibe)
Metallica, Kill em All, 1983
Celtic Frost, Morbid Tales, 1984
Slayer, Hell Awaits, 1985
My Dying Bride, Turn Loose the Swans, 1993