Even this genre can be broken down into other sub genres. Some have a small twist from the original and some are combined with other metal genres. You take a look at these metal bands. The follow are some of the more common sub genres of doom metal.
Traditional Doom Metal
The beginning of doom metal. The 90's was the beginning of doom metal development. Where most old and new bands belong to this group. Doom metal that has heavy distortion and a slower tempo with heavy distortion is usually falls within the Traditional sub genre. You will discover a lot of clean vocals, some high pitched screaming. Reverend Bizarre, Ogre and Witchcraft are a handful of the bands which are in Traditional Doom Metal.
Epic
Traditional metal is almost exactly like Epic metal. The style of singing is what alters the two. There is cleaner singing in Epic metal. Doomsword, Solstice, Candlemass and Solitude Aeturnus are some examples of bands in this sub genre.
Stoner Metal
Stoner is generally known as Psychedelic Doom Metal. The music is known as this because of the psychedelic features that bands include with it. Bands will often use guitar effect pedals and synthesizers to change the sound of the music. You'll see phaser, fuzz and flanger guitar effects within their music. There have been plenty of Stoner metal bands which use various effects. Consider bands like Sleep, Sons of Otis, Acid King, Electric Wizard and Kyuss for more stoner metal.
Sludge
If you put hardcore punk, southern rock and metal all in one you have sludge metal. A fast tempo is very common in this style of music. Sludge metal has more of a raw distortion sound guitar and more double bass drum beats. Singing about society, drugs and politics gives you a concept on what Sludge metal is focused on. Look at Acid Bath, Crowbar, Eyehategod and Grief.
Death Doom Metal
You'll find slow tempos and lots of distortion within this sub genre. You'll find more growling and snarls in this sub genre. This is the most frequent change in this sub category. With increased double bass drumming than typical doom metal. Most bands that fall into this category were influenced by Celtic Frost and Hellhammer. Take a look at bands like Winter, Paradise Lost, Asphyx, Autopsy and My Dying Bride.
Black Metal
Black Doom metal is typical Doom metal using the elements and features of Black metal. High pitched distortion, growls and screams provides you with a nice mixture. Full of dirty distortion along with a slow pace is typical in Black metal. Take a look at Nortt, Gallhammer, Ajattara and Dolorian for more info.
Doom Metal Grows
These are many of the most well known doom metal categories and sub categories that you'll find in doom metal. It started in 1990's and continues to grow today. With metal continuing growing in all genres, power metal isn't any different. Watch for new bands released in Doom Metal.