Weapon arts are back, but are items instead. Generally only limited to specific weapon attack types (slashing, piercing, etc.), weapon art items can also grant separate scaling types to the weapon they’re tied to. Unsure if this means crafting weapons into specific damage / scaling options is gone, but it at least means builds wanting to utilize a specific weapon damage type / scaling are no longer inherently limited to a small pool of weapons. Weapon arts are either used sword + board (shield arts) or two-hander (weapon art).
The maiden grants access to the mount. Mount can double jump, speed up with a sprint via using stamina, allow attacking while riding (melee, ranged, AND magics), and can be resurrected with a life flask usage if killed. Mount feed can be crafted to heal it if need be. Mount is not available in online play, be it co-op or PvP. Mount’s double jump helps to avoid fall damage. Big wind pillar things are available in certain areas to launch you and your mount up to nearby clifftops. Getting knocked off the mount is effectively a death sentence as you have a solid 4-5s animation of writhing on the ground before getting up, all the while being susceptible to damage and enemies doing an execution attack on you.
Character now has a multi-foot-vertical jump. As part of the open world aspect, platforming is greatly encouraged and designed around. Jumping attacks are also present and appear to be fantastic at breaking enemy posture. The distance the player can fall before taking fall damage is WAY further now.
Dark Souls 1 style poise is back, though it appears to be balanced around having Dark Souls 3’s backstab specificity so no autopiloting through hits to cheese your way to a free backstab.
Crouch stealth is here from Sekiro instead of the usual Dark Souls “walk as slowly as possible towards the enemy” stealth. Will be a vitally important gameplay aspect considering large groups of enemies can be common.
Magic is split between miracles (faith) and spells (intelligence). There are pyromancy-esque magics reminiscent of past Dark Souls games, but pyromancy doesn’t appear to be a separate thing and instead is lumped in with miracles or spells (unsure which). Many magics can be charged just like attacks, resulting in things like bigger AoE, better damage, etc. at the cost of no additional FP.
Summon items are now available to bring in one or more monster enemies to fight by your side. Only 1 can be equipped at a time and they’re only usable in specific areas, such as boss fights, dungeons, and notable overworld encounters.
Life and mana flasks are back from DS3, and there’s also a third flask that can be found. It does nothing inherently, but there is a type of items that can be combined together to craft onto the empty flask for unique effects. One example noted in the network test was combining a heal and an explosion effect, resulting in healing yourself then immediately losing a bunch of life to the resulting explosion directly around yourself (does considerably more damage to enemies than to the player). Clearing large groups of enemies or large enemies (like giants) will replenish your flask charges so no worries on your exploration being constantly stunted by having to return to a Grace (definitely-not-bonfire).
Dual-wield power-stancing is back from DS2. Only limitation is that the two weapons need to be the same weapon class (assuming two swords, two axes, etc.?). Twin blade is also back from DS2.
There are various mini-dungeons strewn throughout the world, all having a miniboss and treasure reward at the end. These appear to be the most consistent source of weapon arts, magics, and unique flask crafts.
Successfully blocking an attack with a shield or while two-handing gives a short window for a counter-attack. These counters appear to do great damage, but have a bit of a windup so be careful on bosses and in PvP.
Combat is very much focused on posture breaking like Sekiro. Parries, breaking posture, stunning / knocking down, etc. all can result in guaranteed critical hits and are integrated with all enemies (bosses included).
Leveling can be done at any Grace instead of having to go to a hub to speak to the obligatory waifu. Equipment load is now tied to Strength instead of a separate stat. Stats are Vigor (HP, Fire Resistance, Poison Resistance); Mind (FP, Focus); Endurance (Stamina, Physical Defense, “Robustness” [Bleed / Cold resist]); Strength (Damage Scaling, Equipment Load); Dexterity (Damage Scaling, Cast Speed, Horse Poise, Fall Damage); Intelligence (Damage Scaling, Magic Resistance, Spell Damage); Faith (Damage Scaling, Miracle Damage); Arcane (Luck, Death Resistance, specific spell shenanigans).
There's a Day/Night cycle in the overworld. Some monsters (like giant bats) are active/inactive depending on the time.
Rays of light will be present at Graces to guide the player towards the overarching main story path. This is definitely intended to help those who want to explore every inch of the world and completely forget what they were supposed to be doing after hours of exploring.