Movesets
Polearm Colossals have gotten their own movesets to separate them from the regular Colossals. This includes Golem's Halberd, the Duelist Greataxes, the Erdtree Avatar weapons, Watchdog's Staff and Prelate's Inferno Crozier.
Spears have gotten some love, in the form of a new r1 chain inspired by Wo Long:Fallen Dynasty
Starscourge Greatswords have been completely changed, and now feature a fully dual wield moveset, Unique R2s and a new follow-up to the Unique Skill! (Press R2 after L2)
Ghiza's Wheel has gotten some love too, now it's more like the Whirligig Saw in that every move has the saw spinning! The Unique Skill has gained two follow-ups, including R1 and R2. Ghiza's Wheel is a polearm colossal but it's too unique to be lumped in with the others.
Ice Lightning Slash has gotten an R2 follow-up

Weapon & Shield Catalysts
Yup, weapon catalysts have been fully realized. Now they're able to be toggled on and off so that you can switch between casting and using light attacks. There are also more weapon catalysts. This includes the Carian Knight's Sword, Lazuli Glintstone Sword, Glintstone Kris, Watchdog's Staff, Ordovis' Greatsword, Siluria's Tree, Crucible Horn Shield, Carian Knight's Shield, Scepter of the All-Knowing, and Dragon King's Cragblade.
Shield Catalysts can cast in Casting Mode by double tapping L1 during neutral. Or by doing any attack, then pressing L1.

Inputs
Kick - Flick L3, then press R1. It works the same as Dark Souls 3. The Kick AoW will be changed in a small upcoming update.
Bash - Hold Triangle, then Roll. Deals a fixed percentage of damage, and has different variations based on weapon idle. The Two Handed Shoulder-Rest (Great Weapons) Bash has block frames.
Magic Toggle (Weapon Catalysts Only) - Hold Triangle, then press L3. Toggles between Casting and Normal mode. In Casting mode, R1s are disabled and used for Casting instead. In Normal Mode, the full moveset is available.
Crouch - Crouch now requires you to hold Circle, then press L3. This is a nerf to crouch attack spamming but it helps prevent interference with other inputs.
Double Slash - You can now press R2 to end the combo. 
Ice Lightning Slash - Press R2 for a follow-up attack. You can also cancel into this attack by pressing L2 then R2 immediately after. The attack sends forth a bolt of Ice Lightning at the end of it that can be used as a makeshift projectile.
Horse Riposte - When you knock someone off of their horse, walk up to their feet and press R1 to riposte them. Ghiza's Wheel has something unique for it ;).

Maps
The door at the bottom of Roundtable Hold's stairs has been removed. Head on down seamlessly!

Gameplay Changes and Rebalancing
Jumping and Landing no longer breaks objects
You have more freedom midair
PvP Damage has been reduced by 50% universally
Poise has been completely removed to make way for the Stance Break rework. The PvP (and PvE to an extent) will feel extremely similar to DS3 now.
Hyper Armor has been introduced to more heavy weapon attacks to alleviate the 0 Poise
All Guard Counters now have Hyper Armor
Stance Break rework - Getting attacked enough will break your stance, similar to how enemies get Stance broken. Right now you cannot see your posture bar, unfortunately. Here are the values for Posture that armors have: Light armors - 50 - 65 Posture. Medium Armors - 70 - 85 posture. Heavy Armors 90 - 95 Posture. Bull Goat's - 100 posture. Blocking reduces Posture Damage. Getting Stance broken prevents it from occurring for a short period of time.
Backsteps have Iframes. Iframe amount is based on weight state (Light, Medium, Heavy).
Greatswords have a little more delay between attacks to prevent stunlocks.
The delay between attacks has been removed for all Double Slash AoWs except for Corpse Piler (River's of Blood "Unique" Skill)
You can now turn very slowly during Comet Azur and Crystal Torrent. Have fun :)
All Weapons, except for Daggers can now true combo R1 1 into R1 2. Please give me feedback on this, as I feel the stun might lead to infinites.