I'd like to avoid turning this into a list thread so please type out the reasons why you adore said album and what keeps you interested in it long enough to spin for 24 hours. Anyways, here is my go:

Bathory's Hammerheart-There is a lot to be loved about this album from the epic heaviness to drawn out bombasity, Shore in flames and One Road to Asa bay are the majestic aspects as well as Fire and Ice bringing some crushing riffs.

Neurosis-Through Silver in blood One million different sounds from the monolithic riffs of Locus Star and the self titled, Aeon is the best in my opinion, but with so many sounds its an album that I can spin without getting bored. The tribal aspect of the album is something that I've never heard from any band, and combine that with doom heaviness and you have a trip through the Milky way.

Septicflesh-Ophidian Wheel An album that is interchangeable with Mystic places of the dawn, great leadwork, mesmerizing atmosphere, and an atmosphere that makes you question reality itself. The album itself is strongly Gothic influenced by the death metal aspect is still strong as well

Ancient Rites-Rubicon Combining a rapid tempo with so many folk elements sounds when done effectively adds for a rich experience, and Gunther and company truly outdid themselves on this album. Not to mention some of the epic battle parts such as the intro to Thermopylae and the thrashing tempo of Ypres, the album never gets old after repeated spins.

Skepticism-Alloy In truth, I like Skepticism's latter material much more than their early stuff, the sound is refined and the keyboards add a very otherworldly atmosphere along with the tribal sounding drums.

Lordian Guard-Lordian Guard Easily one of the best epic metal albums I've ever heard with Winds of Thor adding the triumphant intro to an album that epitomizes the familiar Christian legend of God vs Satan. The lyrical content breachy only at certain points but combine the otherworldly atmosphere with brilliant leads, constant melodies, and a soothing voice its an album that is unique as well as one of Tsami's best moments on guitar.

Suffocation-Effigy of the Forgotten Interchangeable with its sibling album Pierced from Within for all intents and purposes as both albums are classics, Effigy's crushing riffs and brutal vocals never get old and the album is crushing each spin. No death metal band since has ever made a riff that tops Liege of Inveracity or Seeds of the suffering, modern brutal death metal begins and ends here.

Black Sabbath-Master of reality One of the heaviest albums I've heard regardless of genre, Children of the grave, Lord of this world, and Into the void are all crushing songs. Add Ozzy's vocals and Solitude and you have a rich and beautiful album that is truly the best album Black Sabbath ever created. Also interchangeable with Paranoid and the s/t

Tiamat-Wildhoney The dreamy soundscapes of this album are something the band would never quite achieve again, as Do you dream of me?, Gaia, and a Pocket Sized sun are all songs that can be replayed with the same bemusing effect. Some call the album gothic metal I just think of the album as a great and spin worthy piece of music.

Cannibal Corpse-Tomb of the Mutilated Once again an album that is interchangeable with its sibling classic albums but more notably Butchered at birth, apart of a few weaker songs such as Beyond the cemetary and Post mortal ejaculation the album is loaded with thrashy pounding riffs. There is a lot going on from Barne's great vocals to the full out intensity of Hammer smashed face and Necropedophile.

Doomsword-Let Battle commence In truth one of the few Epic heavy metal albums I can tolerate without being bored, mainly because the vocals are incredible and the riffs and atmosphere are truly reminiscent of battle. There isn't much else to say about the album

Inquisition-Into the infernal regions of the ancient cult While I love Under the Sign of hell and De mysteriis dom Sathanas, the sheer amount of thought and evil atmosphere conveyed on this album trumps both. From dark acoustic passages to the creepiest black metal vocals I've ever heard, each song is unique and the album never ceases to amaze me with its mini-universe of sounds. In truth, its probably the only black metal album you'll ever need really.

Moonspell-Wolfheart The rich gothic atmosphere combined with the bands last flirtations with melodic black metal make for a unique album, not to mention songs such as Alma Mater just kick ass.

Honorable mentions: Dark metal, Destroy the Opposition, Blood, fire death, Close to a world Below, Thyrfing, Psalms of the Moribund, Autumn Aurora, Annihilation of the Wicked, Electric Wizard, Immortal Pride, Ultima Thulee, Epicus Doomicus Metallicus, Storm of the Light's bane, Hordaland's Doeksvad, My soul for his glory, Warning and many more.