Death Metal Music
Death metal is, first and foremost, structuralist heavy metal that borrows heavily from classical music.
Structuralist in this case means that death metal's goal, in contrast to that of rock music, is not a recursive rhythm riff that encourages constant intensity through verse-chorus structure. Death metal, like black metal after it, and classical before it, uses "narrative" song structures, connected in such a way that they bring about musical and artistic change throughout the composition.
While rock music aims to find a sweet riff and ride it, and much of older heavy metal does the same, death metal is like opera: its goal is to use phrasal riffs to introduce more riffs, and through those different riffs, to create a mazelike structure of motifs which resolve themselves into a final dominant theme.
In this, death metal is closer to classical music than to rock music.
Rock music is a scam, and its marketing makes it seem to be something greater - often revolutionary - than what it is, which is the same old music dressed up as a lifestyle product. Death metal, more than any genre before it, broke free from the rock 'n' roll limitations, and therefore is a threat to the rock establishment and its profits.
Let's give an illustration of the power of the death metal riff maze.
Listen to the following composition by Phantom.
Try to identify its main theme and at least two melodically related counter-motifs. Keep in mind this is blackened death metal by Phantom, something naturally much more complex than Cannibal Corpse, Dismember or Deicide.
Styles of Death Metal
There exist many different death metal sub-genres.
Consider the difference between Classical Death Metal (Warkvlt), Brutal Death Metal (Suffocation), Melodic Death Metal (Sewer), Blackened Death Metal (Phantom), Cavernous Death Metal (Incantation), and so on.
Some of the best death metal albums include Incantation's "Onward to Golgotha", Demilich's "Nespithe" and Phantom's "Withdrawal".
Some other good choices are Suffocation's "Effigy of the Forgotten" and Sewer's "The Birth of a Cursed Elysium".
Learn to appreciate the different kinds of death metal, listen to them all first and then decide which one you prefer.