one of the many forms of "extreme metal" alongside genres such as black metal and grindcore, death metal is characterised by heavily downtuned and distorted guitar riffs, extremely fast drumming (drum patterns such as blastbeats
are often used, and harsh, guttural low pitched vocals, occasionally alongside high pitched screaming.
death metal comes in many sub-genres: brutal, technical, blackened, melodic, deathcore, etc etc, with the most "mainstream sound" coming from more melodic bands such as in flames or arch enemy.
brutal is a genre that is commonly associated with bands such as cannibal corpse, hate eternal and devourment. this is arguably the most heavy form of death metal with heavily downtuned guitaring, frequent blastbeats and extremely harsh guttural vocals. subject matter ranges from rape to necrophilia and everything in between.
technical/progressive death metal is a subgenre most commonly recognised by its extremely technical guitaring, with frequently changing song structures and uncommon time signatures. Examples include Necrophagist, Cryptopsy and to some extent Opeth.
Blackened death metal is a sort of fusion between death metal and some of the more melodic aspects of black metal, aswell as the subject matter such as satanism, the occult and general evil. Some early influences to the subgenre include deicide, immolation aswell as black metal bands such as marduk, bathory, burzum and mayhem, and prime examples of the subgenre are bands such as Behemoth, belphegor and zyklon.
melodic death metal is a fusion of heavy metal, death metal and other musical genres. The genre includes less harsh vocals although guttural growls are used sometimes, as well as blastbeats and uses downtuned/ distorted guitars less liberally. Started in scandinavia, or more specifically Gothenburg, Sweden, with the first bands that dubbed the genre as the "Gothenburg Sound". Pioneers of the genre are namely in flames and at the gates, and other examples include dark tranquility, amon amarth, arch enemy, entombed and nihilist.
deathcore is a fusion between death metal and "metalcore". As metalcore became more popular thanks to bands such as killswitch engage, other bands began to fuse metalcore already heavy aspects with a more death metal orientated sound; for example job for a cowboy. Many deathgrind bands are confused for deathcore.
deathgrind is a fusion between death metal with certain aspects of grindcore, such as the high pitched screaming, complex song structures and irregular time signatures. Some examples of deathgrind include cephalic carnage, pig destroyer, rotten sound and annotations of an autopsy.