Wow, that UG article was fucking dumb. But if you want a list of the stern genres:
* = Concrete sub-genre
+ = Fusion Sub-genre
- = sub-sub based off an ambiguous idea, usually described in it's name (ie Technical riffing or bombastic Viking Marches)
Main Metal Genre's*Heavy Metal
*Speed Metal
*Doom Metal - Chunky, slow/mid-paced ominous riffing, focusing on minor melodies, generally with a melencholic or epic atmosphere. Most popularized by the first four Sabbath Albums (think the title song, Black Sabbath)
+Death/Doom and Dark Ambient = Funeral Doom Metal
+Drone = Drone/Doom Metal
+Gothic Rock = Gothic Metal
*Sludge Metal (Doom + Hardcore Punk aggression, simplicity and rawness)
+ Sludge + Post-Rock = Post-Metal
*Stoner Metal (Doom riffs + Psyche Rock lead playing, with fuzzy, stony atmospheres and Hard rock balls and attitude)
*Thrash Metal (Speed + Hardcore Punk)
+more Hardcore Punk = Crossover Thrash
*Groove Metal/Post-Thrash (Thrash + NY Hardcore. Pantera, more or less. Dumbed down, chunky riffing but with smashing thrash drumming)
*Power Metal (Speed metal with heightened melodic and epic sensibilities. utilizes soaring, clean vocals, with tons of duel leads and Beer-hall like choruses. Think Iron Maiden on crack)
*Death Metal
-Technical Death Metal
-Brutal Death Metal (Death Metal that focuses on extremely heavy, rhythmic assaults, with incredibly low, guttural growls)
+Metalcore = Deathcore and viceversa
+Heavy/NWOBHM = Melodic Death Metal
*Black Metal
-Viking Metal
+Post-Rock/Shoegaze = post-Black/Blackgaze
+Ambient = Ambient Black Metal
*Folk Metal (Black/Power/Melodic Death + Folk music melodies and rhythms. Generally there's an emphasis on catchy and beer-hall-like choruses of power metal with black metal's aggression, occasional vocal style and heathen imagery with melodic death metal's heaviness and production. Albeit, some bands may lean more towards one of those three genres. )
-Pagan/Celtic/Viking/Medieval/Oriental/Pirate Metal are often lumped into this category.
Genre's with unspecific Metal bases:*Symphonic Metal (generally applied to Black, Power, Gothic/Power, Death and Folk Metal that use their respective riffs around grand, Midi symphonic orchestrations.)
+Industrial/Industrial Rock + Metal = Industrial Metal (Generally applied to Thrash, Groove, Black and Death. Uses robotic speed and drumming, distorted vocals, while also using tons of clipping and sampling.)
+Progressive Rock + Metal = Progressive Metal ( Death, Power, Heavy, Sludge, Black that uses all or some of the following features: odd time signatures, rarely repeat riffing/songs are extensive, connecting concepts, technical guitar playing, complex song structures, often using keyboards and soundscapes and generally pushes the boundaries of said genre. )
Associated, but generally not Metal genres:
*Grindcore (Powerviolence/Hardcore Punk + Death metal)
*Crust Punk (Powerviolence/D-Beat + Black/Thrash/Death metal)
*Metalcore (any combination of metal and hardcore, if the band leans towards metal it is metal, if it leans towards hardcore, it's hardcore. Trivium, LOG and DRI are metal while Atreyu, Converge and Everytime I Die are not)
*Alternative Metal (Alternative Rock + Groove/Post-Thrash/Industrial Metal)
*Nu Rock/Metal -originally known as Aggro-Rock- (Alternative/Funk Rock + Alternative Metal + Hip-Hop)
*Industrial Rock (mistaken as Metal, but an offshoot of Industrial music and alternative Rock)
*Hard Rock
*Proto-Metal (Psychedelic/Hard Rock)
Slight variations on Sub-genres that are ultimately not really full sub-genres. *NWOBHM: A term used to describe Metal bands formed from Britain from 1978 to around 1986. Bands ranged from Traditonal, Speed, Black and Doom metal, so it can't really be described as a genre and more like an time and places specific aesthetic.
*Depressive/Suicidal Black Metal: generally just black metal based around depression and suicide. It's only real defining trait is a common use of a tortured howl-vocal style.
*Bestial/War Black Metal: I'm not 100%, but I seem to see it as a type of black Metal that fuses the rawness of black metal with thrash's drumming and death metal's brutality.
*Epic Doom Metal/Epic Anything Metal: Tends to just mean some sort of Trad/Power metal influence in the vocals, lyrical content and mood.
*Euro Power Metal: Power metal that usually lies towards extremely melodic, crystal clear power metal like Stratovarius, Gamma Ray and Sonata Artica .
*US Power Metal: Mostly means Power metal with a dash of thrash edge and aggression, mostly like American bands Metal Church, Iced Earth and Jag Panzer
*Dark Metal: I personally have my own definition of the genre, but it has been used to describe a multi-tude of metal styles (and what would one expect with such a synonymous term with metal). My general understanding of it is a mixture of doom and black metal, with some sort of added ambient/atmospheric element. Recently, I and others have used the term to describe bands that mix Black/Doom with neo-folk music, such as Agalloch, October Falls and Flight of Sleipnir, but it's still quite ambiguous.
*Djent: is a type of Technical/progressive Metal or Metalcore that focuses on heavily digitallized and distorted
guitar tones from processed power chords, with elastic, start-stop syncopated guitar riffs often interwoven with polyrhythms.
*Glam Metal: More or less just Heavy Metal (Motley Crue, Dokken, Twisted Sister), but more commonly just Hard Rock (Posion, Cinderella, Faster Pussycat), that emphasizes on pop hooks.
*Death N Roll/Black N Roll: Death or Black metal that adds hard rock inspired sounds, aesthetic and riffs. I don't know, maybe these deserve their own spots as genres. Then again, on listening to most of it, maybe rather not...
*White Metal/Christian Metal: Just pro-Jesus Metal. Not really different at all except lyrical content. "Hank Hill (in this case to Stryper): "Can't you see you're not making Christianity any better, you're just making Heavy Metal worse."
*Slam Death Metal: A type of Brutal Death metal that focuses on "slammy", slower, smashing palm-muted riff breaks.
Edit: added a fuckton of stuff on