Prior to this album, "doom" did not exist. A few Black Sabbath clones, and even Sabbath itself, are considered pioneers of this art form, but I can present a strong case to the contrary.
Unarguably, Black Sabbath invented what we know as heavy metal. No one before them sounded like they did. However, only a few of their songs could be considered to meet the requirements, musical and lyrical, of "doom"--"Electric Funeral" from Paranoid is a prime example--but as their career progressed, they failed to capitalize on this trend and got stuck in a heavy rock sort of vein. Even when they reinvented themselves in the 80s and regained some heaviness they did not duplicate the dark, evil sounding riffs.
Candlemass does NOT sound like Black Sabbath. Candlemass is the origin of doom metal. Period. A few earlier bands attempted it on a song or two, but Candlemass was the first to perform such a style throughout an entire album and in the process formed their own brand of music: Heavier, darker...They even gave it a name: Epic Doom Metal.
Quite simply, Candlemass is the pioneer of DOOM as a musical religion, and this album is the blueprint for the genre for all time. No one can dispute this.
Every song is a dark lament. Every song is a dirge for forsaken lives and fading hopes. Nothing since has come even close, even the godly Candlemass albums which followed. The line-up on this album did not stay together, which is a shame. The singer is the premier doom vocalist, with his mournful, haunting delivery of Leif Edling's suicide letters and tales of undying despair. His replacement on subsequent albums, while an adequate vocalist, brought an unwelcome element of ham with his operatic histrionics. And the drummer here is outstanding. Check out his fills on "Demon's Gate".
Epicus Doomicus Metallicus to this day remains unchallenged in its position of DOOM supremacy. Even Candlemass themselves could not have topped this. Other albums are called "the best doom metal blah blah blah...". Uh-uh. Those are sales pitches. This is the real thing.