Here's a detailed list from HungryGhost57 on the article and what it mentions, get ready.
All new info: Started working on game before unity Brand new fighting system New A.I. No minimap but a elder scrolls type compass at top No more sprinting button, speed depends on analog stick Crouching is back Story is being kept a secret Eagle vision is a subtle pulse that highlights objects not enemies Takes place during the ascent and reign of cleopatra You can climb everything in the game Large and small cities with many landmarks including Memphis and Alexandria The controllable eagle leak was true NPC's have a day/night cycle and includes time for them to eat, sleep, work, and "answer the call of nature" Attack buttons are the right shoulder and trigger A.I. does not take turns to attack New combat system is more hit-box driven As you fight, an adrenaline gauge fills up, and when both attack buttons are pressed powerful attacks are unleashed Left shoulder button is lock on There are treasures to find in the depths of the water (sunken ships, long-forgotten ruins) Stat element of customization is removed New gear system where players can improve specific parts of your gear by crafting materials Leveling system that has a level cap of 40 Bayek is not the only playable character in the game but that character is a secret There are legendary items to loot in the game You can add blocked arrows to your inventory You can no longer one hit enemies that are more powerful than you with your hidden blade Buttons for free-running up and down are removed Puzzles are back but more challenging and less switches Much more in depth ability graph with 3 paths (Seer, Warrior, Hunter) There are gladiator battles in arenas