Every time I listen to Morbid Angel's Covenant, I think it is pretty much the best death metal album, with the best death metal sound, ever. Altars of Madness is an indisputable classic, yes, and Blessed are the Sick is a great album, but for me Covenant defines death metal and its brutality, dissonance, occult atmosphere, etc. Every aspect of the album is perfectly honed. There are certainly rawer, more influential albums, albums more important to the origins of death metal, but to this day I think of Covenant as the standard which, for my tastes, all death metal must aspire to meet.