So for combat, you got a pistol(with proper aim down sights this time), a shotgun,(NG+ gives an optional sight that increases damage but reduces accuracy) a knife, frag nades, incendiary and nitro(stun) nades.
The main big change is a straight up parry if you time your block as a strike lands on you. Timing is odd at first but you get a decent window of opportunity but timing is legit. Rewards are that an enemy gets staggered for a follow up strike, with a good ol' FI$T or a B00T to a grounded foe that typically instant kills, staggers other foes if near(potentially leading to other stunned foes) and seems to have some sexy I-fames we know and love(does suplex to priest). A headshot will usually put a standard molded into a stun state, stun nades but mobs into a melee state, also you can stomp grounded foes even if they are not stunned.
You can parry practically any attack(including the bosses), it's super satisfying to just repel a move you could only block in the base game, the crawler/*not* lickers jumping flailing attack gave me trouble as it can sort of clip or break your guard.
The game demands you learn this on professional mode, as you have very little ammo compared to normal, and only start with a knife. Some enemies *White molded* can only be harmed via special ammo for the pistol, but can be stunned with parry/prompt follow up or grenades.