Black :
# Lyrics, often taking the form of Satanic themes which blaspheme Christianity, and other occult themes, like paganism (this is the hallmark of Black Metal, but is not exclusive to it. Bands such as Slayer, Deicide, and Immolation overlap lyrically with black metal somewhat, but are generally not referred to as black metal)
# heavy distortion
# fast, aggressive drums, often including blast beats
# fast, repetitive guitar playing (so-called tremolo picking, in which the guitar is played similarly to balalaika) and riffing
# high-pitched screeching vocals
# swift percussion
# repetition
# cold and sad atmosphere.
Death :
Death metal is usually identified by extreme brutality, intensity and speed. "Blast beats" are frequently used to add to the intensity of the music. The vocals - death grunts, (guttural roars) or "growls", as they are often called, are rough and often incomprehensible (sometimes derisively called "Cookie Monster vocals" by those who dislike this vocal style). Similarly, those not familiar with the genre sometimes confuse it with "death rock", which is an entirely different musical classification altogether.
Doom :
Instrumentation
Like most kinds of metal, doom metal is typically based on vocals, guitar, bass guitar and drums, and heavy guitar riffing is considered an essential part of almost all of its subgenres. A large number of doom metal bands, especially newer bands, use keyboards as well; in classic doom, however, keyboards are still relatively uncommon. A number of doom-influenced gothic metal bands such as My Dying Bride or Funeral have also made use of violins.
Traditional doom
Slow, melancholic, riff-based metal influenced by Black Sabbath as well as the NWOBHM movement. Typical examples: Saint Vitus, Pentagram, Candlemass, Solitude Aeturnus, Reverend Bizarre, Solstice, Warning, Solomon Kane. A significant borderline case are (early) Cathedral, who are considered a traditional doom metal act by some and one of the originators of the modern death/doom sound by others. Four "waves" have so far been recognised in the history of traditional doom: the first one started with the originators of the entire genre, the proto-doom bands Black Sabbath and Pentagram; the second one has been located in the mid-80s, especially in the work of Saint Vitus; the third one started with the success of Cathedral's debut album Forest of Equilibrium; the fourth one has recently been affiliated with Reverend Bizarre.
Death/doom
A mixture of death metal with some influences from the classic doom metal sound. Typical examples: Winter, Unholy, (early) Paradise Lost, (early) My Dying Bride, (early) Anathema, (early) Katatonia, Disembowelment (with some other influences). A significant borderline case are (early) Cathedral, who are considered a traditional doom metal act by some and one of the originators of the modern death/doom sound by others.
Funeral doom
Funeral doom is an even slower and more basic version of doom death. Funeral bands take the slowness of doom metal to an extreme and emphasize on an atmosphere of despair and emptiness. Pioneers of this style were Thergothon, Skepticism, and Funeral, and modern examples include Shape of Despair, Stabat Mater, Mournful Congregation, Dimness Through Infinity and Until Death Overtakes Me.
Drone doom
A style which is even more basic than funeral doom, drone doom is generally influenced by noise and ambient. Vocals and even drums are often absent, and the music often lacks any beat or rhythm in the traditional sense. Heavy use of feedback is also typical. Like funeral doom, drone doom typically emphasizes despair and emptiness. Innovator Stephen O'Malley, heavily influenced by Earth, can be largely credited with the creation of drone doom as a recognised subgenre, being or having been involved with seminal acts such as Burning Witch, Sunn O))) and Teeth of Lions Rule the Divine. Typical examples: Sunn O))), Earth, Khanate, Orthrelm.
Stoner doom
A hybrid form of doom metal and stoner rock. Typical examples: (late) Cathedral, Sleep, Unearthly Trance, Grand Magus. A significant borderline case are Electric Wizard, who confusingly balance between traditional doom (according to themselves), stoner doom (according to the press), and sludge doom.
Atmospheric doom
An often less heavy and generally more melodic kind of doom metal, often with female vocals. Typical examples: (late) My Dying Bride, The 3rd And The Mortal, Avrigus, and The Gathering.
Sludge doom
Combining the thick, riffing sound of stoner doom with the raw abrasiveness and shrieked vocals of hardcore, sludge is at the outer limits of doom metal and is an acquired taste (although a couple of bands, such as Eyehategod and Crowbar, are fairly well known within the metal community). Even though many sludge bands sport the "booze 'n' bongs" image synonymous with stoner rock, they lack the stoner rockers' positive outlook on life. Typical examples: Eyehategod, Crowbar, Grief.
Industrial doom
An offshoot of various doom-metal genres (mostly doom/death) and sludge, but based on the industrial sounds of bands such as early Godflesh, Skin Chamber and early Swans. It is characterised by heavy use of electronic sounds, such as samples or pounding drum machines, with the more traditional guitar on top. It is mostly atonal and dissonant, and usually avoids melody. Typical examples: Zaraza, Wraith of the Ropes, Philistine.