Thankyou to The Xtortionist and Neiteio for their contributions which I've edited.
Melee is much more the focus of combat in RE6 and using it well is the key to success. Players who don't roll, slide, quick shot, etc... are going to have a horrible time with the game.
Here's a quick list:
-Aim+Melee - Quick shot - these are a kind of auto aim attack great for crowd control and stunning enemies to set them up for melee attacks.
-Aim while sprinting - Slide (Will stun enemies. Can slide into cover and keep Aim held down to stay in cover)
-Slide+left stick down - 180 slide
-Sprint+Melee - dash attack - You can use this shoulder-check to stagger enemies and set them up for further melee attacks.
-Aim+Direction+A(360)/X(PS3) - Dodge roll (hold Aim to stay on ground, can 180 when dodging forward and pulling back on left stick. Can simply duck if not holding a direction. Can cancel duck into a dodge). Releasing L1 the moment you hit the ground causes you to hop back to your feet. Holding L1 will allow you to shoot from the ground. Tapping left or right will cause you to roll in circles around your enemy.
-You can do the backdepleted version of the above the moment you're hit to the ground by an enemy hold A/X (solo action) button to instantly roll back to your feet. Also note you'll be knocked over every time a segment of your health bar is fully depleted.
-Lying on the ground will make it harder for some enemies to hit you, and easier for you to hit shorter, low to the ground enemies. While lying press back or forward to slowly drag yourself along the ground in that direction, good for throwing off enemy aim after falling backwards.
Counter attack
-press Melee just as an enemy is about to attack/hit you to counter. Sometimes there will be no prompt for this until you have performed the counter, other times it will be very fast. Timing is very important.
Melee attacks
-Your Melee attacks are governed by the Stamina Meter, use too many Melee attacks in a row and it will be drained and "overheat".
-Keep an eye on your stamina Meter, taking cover will refill it faster (so will lying on the ground without moving).
-You can disarm armed zombies by hitting them twice with a melee, which dazes them so that the third melee wrenches the weapon out of their hands and kills them.
-You can melee enemies standing behind you, elbowing them in the face to stun them, setting them up for a different melee.
-Enemies staggered in a certain way will also spin, context-sensitive melee them from behind for a kill animation like a neck snap.
-You can guarantee the context-sensitive melee by shooting an enemy in the head just once to daze them, then getting close and hitting R1.
-Some larger enemies can be attacked while in certain states to trigger QTE chain combos. For example the lizard-like Strelats can be melee or dash attacked to trigger a combo while they're turtling inside their fans before shooting their spikes.
Weapons
-Weapons have their own unique attacks and combos (hold aim and continue to tap attack after quick shots for certain characters/weapons). Chris's knife for example does a multi slash by aiming and tapping back + A/X (solo action) button, great for fending off advancing enemies.
-(Jake's Hand to Hand) Hold Aim until target is acquired, then mash Melee - Three hit combo
-(Knives only)
-While aiming, left stick down+Melee - Stab attack
-While aiming, left stick left or right+A/X(solo action) button - sidestep
-Y/Triangle while aiming certain weapons - Select fire mode
*Can quick shot with knives and grenades
*Stagger system still in effect. Headshot a humanoid enemy to stagger them, then perform a contextual melee (front or back) for massive damage.
-Remote Mines and grenades must be equipped by tapping up or down on the D-pad, and can only be deployed one at a time. After deployment you will revert to your previously equipped weapon.
-Remote mines can be deployed while sliding, and all grenades can also be thrown while on the ground
Other Tips
-Rotate both sticks during grappling QTEs, the game responds to both inputs and it makes them easier.
-You can paint enemy targets for your AI partner to priortize by aiming at the enemy and tapping B/Circle.
-Hold Heal and reload - to Auto Reload the pill container from the available herbs in your inventory without having to enter it.
-A pill will recover your stamina as well as a single block of your health.