List of Brutal Doom features

WORLD:
Implementation of headshots for all monsters, except the Cacodemon, Lost Soul, Pain Elemental, and Arch Vile. Headshots deal as much as double damage (depending on the weapon), and can gib the monster's head for one of many special death animations.
Enormousness increase of blood and gibs to make a gorier and more violent atmosphere.
3d bloodspots allow all textures to be covered with blood, including the floor and ceiling.
Blood will be displayed on the screen if the player kills an enemy up close.
Fake cracks and/or bullet holes may appear on the screen when you get injured.
New death animations for all enemies. Body parts can be torn apart by regular fire on various locations on the enemy's body, cut in half with the Chainsaw, or melted with the plasma gun.
When small enemies such as zombies and imps are hit in close proximity to an explosion, the enemy is dismembered and trowed away in a way that simulates a ragdoll psychs effect.
When enemies are directly hit by rockets, the enemy is reduced to a large pool of blood and guts in a
massive explosion.
Corpses can be further mutilated upon death.
Some corpses can be pushed away by kicks and punches in a way that resembles ragdoll psychs.
If you kill some monsters with the chainsaw or rocket launcher, you can pick up their weapons (for example, the Mancubus' flame cannon or the Revenant's rocket launchers).
Most weapons cause kickback. Especially, the Super Shotgun, when firing both barrels at once.
Most weapons must be primed and reloaded. The player can assign the reload button to a specific key, though after a specific number of shots the weapon will reload automatically.
The player's ammo capacity for bullet weapons has been increased from 200 to 300 (and from 400 to 600 with a backpack).
Enemies may randomly drop beserk packs upon death.
Barrels and other explosives expel smoke upon detonation.
Enhanced lighting and shadow effects for decorations and projectiles similar to the Doomsday engine.
Enhanced liquid textures.
Marines and monsters now wade through a liquid instead of walking on it, also wading through liquids causes a splashing sound to be played. This also happens to liquid, when a marine or a zombie shoots it.
Lights can be broken by gunfire.
Weapon sound effects are added, such as ricochets and casings bouncing.
Shooting bullet weapons close enough to a wall will cause you to be hurt by shrapnel.
Weapons have smoother animations.

MONSTERS:
Barons of Hell, Imps, Demons, Cacodemons, Revenants and Hell Knights will perform fatalities on the Player and friendly marines if they kill him with a melee attack.
Barons of Hell will perform a fatality if they kill imps, demons, and zombies in an infight.
The zombieman has 50% of chance to fire his gun 3 times during his attack instead of 1.
Shotgun guys fire 5 pellets at a time instead of 3.
The Imp has a leap attack similar to the in Doom 3.
The Cacodemon can shoot two projectiles in a short amount of time, and can shunt itself out of the way of incoming attacks.
The Baron of Hell has an attack where it can launch 3 projectiles in a wide spread instead of one.
The Cyberdemon gains a new melee attack: a devastating stomp, which against the player is almost always an instant kill
The Spider Mastermind's minigun is now a high-calibre rotary cannon loaded with exploding rounds.
Pain Elementals now explode upon death, causing often fatal damage to the player and nearby monsters.
Wolfenstein SS Nazis will drop their MP40 sub-machine guns upon death, which the player can use for himself (see Weapons section).They are also much smarter than the Vanilla counterpart, they fire longer fire bursts, and will attempt to dodge enemy's attacks with circlestrafe.

PLAYER ABILITIES
Using the Berserk Pack, you can pick up Lost Souls and Barrels and throw them.
When a berserk pack is collected, barrels can be picked up by alt-firing with the fists while aiming at them. The regular attack allows it to be thrown at an enemy, while the alt-fire drops the barrel to set it as a trap.
Also using the Berserk Pack, you can pick up stunned Former humans and Imps (a "stunned" monster will have had its arm or leg blown off and be kneeling on the ground) to use as meat shields against projectiles. This restricts the player to the assault rifle, but the meat shield can be thrown for extra damage at any time.
A kick attack has been added to push enemies away from the player, similar to Duke Nukem 3D. It can be bound to a specific key.
If you jump before kicking, you will perform a flying kick, which deals three times more damage, but this movement usually turns you very vulnerable.
You have the ability to flip monsters off by a bindable command known as "Offend." This command will alert nearby monsters as if the player had just fired a weapon.
You have the ability to wave by a bindable command known as "Wave." Pressing the wave button during a fatality (see below) will allow the player to see his own wave animation in third-person.
Punching a Zombieman, Shotgun Guy, Chaingunner, or Imp from behind before the enemy has noticed the player will cause the marine to snap the enemy's neck, killing the enemy instantly without alerting other enemies.
Sprite change of rockets and box of rockets, backpack, armor bonus, armor and megaarmor.
Invisibility spheres are replaced with captured marines. If the player punches or kicks the marine, he will be freed and will attempt to fight against the demons. The captured marines hold random weaponry, with multiple playthroughs of a level resulting in differing weapons that the marine will fight with. After the player spots the captured marine, the demons around the captured marine will
attempt to kill him before the player can free him.

WEAPONS
Weapons have +NOAUTOAIM flag to prevent autoaiming for headshots.
The fists are faster and can make quick jabs at enemies. They are also a silent attack and will not alert enemies. The alt-fire launches slower but more powerful hook punch.
The fists' reload has the Doomguy crack his knuckles, while it normally does nothing. It switches between "Rip and Tear Mode" and "Smash Mode" after acquiring a berserk pack. Smash mode punches monsters to pieces. Rip and Tear mode does fatalities.
The chainsaw uses the Doom 3 Chainsaw sound effects and blood splatters on it, when sawing an enemy. The blood disappears, shortly, after that.
The shotgun has black synthetic grip and pump handle instead of wooden ones, and also has a vented heatshield on the barrel. The shotgun also fires ten pellets per shot to match the Super Shotgun's 20.
The pistol is replaced by an assault rifle, which unlike the original pistol remains useful even late in the game. The combat rifle has a decent fire rate and is one of the most accurate weapon in the mod. The alt-fire mode allows the player to aim down the sights to snipe enemies. The combat rifle must be reloaded after 20 shots.
The Super Shotgun has a slower reload time, but at point blank range will deal an additional damage boost. Alternate fire will fire one barrel at a time, each firing ten pellets.
The chaingun is replaced by a minigun, which fires 50% faster but also requires a spin-up and cooloff before and after firing respectively, similar to the plasma gun. The alt-fire mode makes the barrels continuously spin, decreasing the spin-up time before firing, but also decreasing the accuracy and alerting monsters.
The rocket launcher has a slower rate of fire but causes double more damage on a direct hit. It must be reloaded after 6 shots.
The plasma gun now deals double damage, can cause splash damage to enemies (and players, if the bolt hits a wall). The alt-fire mode allows the plasma gun to fire a spread of plasma bolts in a shotgun-like spread, which can do as much damage as two rockets. The plasma gun must be reloaded after 50 shots.
The BFG9000 uses the sound effects from the Doom 3 version, and the primary energy ball deals double damage as well large splash damage. The Player will not suffer any splash damage if the bolt hits an enemy directly.
The MP40 has a higher rate of fire than the assault rifle and a 32-round magazine, but unlike the assault rifle the player cannot use the iron sights.
In the Skulltag version, both the grenade launcher and the railgun have been given new sprites and attributes. The grenade launcher is a standard M79 grenade launcher with much larger blast radius than the rocket launcher. The railgun fires at a slower rate than the Vanilla Skulltag railgun but uses half as much ammunition and reloads after 10 shots instead of 4.

The Flamecannon can be harvested from a Mancubus dead body by using a chainsaw.
This weapon fires large fireballs that deals medium splash damage over a large area. Not powerful against high tier monsters, but it's very efficient to destroy cluster of low and mid tier monsters.

The Hellish Rocket Launcher can be harvested from a Revenant dead body by using a chainsaw.
It fires explosive homing fireballs. It can deal considerable damage, and due it's homing feature, it's a nice weapon to destroy Cacodemons trying to dodge attacks.

More info on:
Doom.wikia.com