Death metal usually includes but is not limited to fast riffage, growling vocals, and blast beats. Modern death metal has some grindcore influence. Yes, it does take talent to vocalize like that. Record yourself "growling" and let's see how professinal you sound.
The following band is not death metal: Slipknot. Slipknot is mallcore. Deal with it.
Possessed's use of abrupt tempo changes, gutteral vocals, unusual phrasing and Satanic overtones separated them from the more light hearted, punkish sound of thrash metal. The death metal template would continue to develop as Necrophagia, Death, Morbid Angel, Obituary and Autopsy released their respective debuts. These groups generally focused on horror-movie inspired blood and gore as well as occultist themes. By the 1990s, death metal had exploded in the underground and a number of influential bands rose to prominence. Additionally, if anyone wanted to call themselves death metal, extreme distortion, low guitar tunings and excessively fast tempos were mandatory.
Cannibal Corpse, Suffocation, Dying Fetus and Deicide presented a percussively driven flavor of death metal, while Death, Cynic, Hypocrisy, Atheist and others prided themselves on more intricate and melodic guitar work, as well as lyrics dealing with social and political issues. Among the most extreme bands included both major Disgorges (USA and Mexico, respectively), Devourment and Mortician, who focused on very low tones, both in the guitar tunings and vocal approach. This was in direct contrast to melodic death metal bands such as At the Gates, the later work of Carcass, and In Flames, who often explored tones above middle C, rather than primarily or exclusively focusing on the bass strings.
The accessibility of melodic death metal (and the public's exposure to increasingly aggressive rock) has lead to deathcore, in which groups such as Job For a Cowboy, Winds of Plague and the recent work of Cryptopsy combine the death metal aesthetic with modern hardcore and other accessible styles.
There are a number of other fusion styles that have developed over the years, including the black metal/death metal hybrid "blackened death metal" (Archgoat, Angelcorpse, Blasphemy). Deathgrind or death grind combines death metal with grindcore (Aborted, Circle of Dead Children, Origin). There are also experimental groups such as Portal, Gorguts and Negativa, who use death metal as a basis to explore a number of unusual rock stylings.
Death Metal is catergorized by its gutteral growling vocals, thickened guitar tones with sometimes heavy distortion properties, and blast beats which can range from a normal to very fast speed. The vocals and drumming are the pure tell-all of a death metal band, the gutteral bellows are began in the stomach yet shaped with the throat to raise and lower the pitch of the music in general, while the drumming is blast beat and dependant (mainly) upon the bass drums. Independant variables to be added to the mix are amounts of groove, morbidity, technicallity, and speed.
Death Metal itself has evolved slowly through the years, ranging from the olden days (Deicide, Death, and Morbid Angel) to the now modernized sounds of Death Metal, (Vital Remains, Cryptopsy, and Hate Eternal) and even now to the more "Brutal" scene of Death Metal (Deeds of Flesh, Severed Savior and Beheaded). Death Metal also has grown roots into the Grindcore scene and evolved many Death/Grind bands, evolved into Gore Metal, and numerous other forms of music.