Anything by Anacrusis! Very overlooked band that was years ahead of it's time.
Black Sabbath - Born Again
Leatherwolf - S/T
Angra - Fireworks
I fully support these posts.
I don't know if underrated is the proper tag, but albums that I found no one talk about or seldom mentioned:
Iron Maiden - "Killers"
Abbatoir - "The Only Safe Place"
Motorhead - "We Are Motorhead"
Acid (all albums)
Quartz (all albums)
Meliah Rage (almost all albums)
Alice Cooper - "Goes To Hell"
Armored Saint - "Symbol Of Salvation"
Black Sabbath - "Headless Cross"
Bruce Dickinson - "Skunkworks"
Candlemass - "Death Magic Doom"
Hawk - "Hawk"
Hawaii - "The Natives Are Restless"
Culprit - "Guilty AS Charged"
Death Angel - "The Art Of Dying"
Kreator -"Endorama"
Forte - "Rise Above"
Wolf - "Edge Of The World"
Black Knight - "Master Of Disaster"
Halford - "Made Of Metal"
Metal Church - "Hanging In The Balance"
Lordian Guard - S/T
Ostrogoth - "Full Moon's Eyes"
Pretty Maids - "Pandemonium"
Riot - "Sons Of Society"
Venom - "Prime Evil"