The album, originally titled None More Negative, launched the band's career. The album has a rawness that was prominent in Peter Steele's previous band, Carnivore, but it incorporates elements that became standard for Type O Negative, merging styles including doom metal, gothic rock, new wave and industrial music. Slow, Deep and Hard is a semi-autobiographical album with heavy amounts of black humor, based on a relationship in which the vocalist/bass guitarist Peter Steele was involved. In keeping with the band's notable humor, the cover of Slow, Deep and Hard is of a blurred out picture of sexual penetration.
Piero Scaruffi, a music historian, has called the album the best heavy metal album of all time, giving it 9/10.