In short. With CK3:
1. Making the map more detailed. The Baronies and towns are not just slots in the county menu, but they're on the map. More intuitive, more strategic.
2. Expanding significantly on the most popular features, including RPG elements, dynasty building, and emergent storytelling. AI characters will react to situations according to their traits rather than according to a flat RNG generated a response.
3. The reason for CK3 is that CK2 became very difficult to work on. In my personal experience, I lost saves from updates, and it became more common in the last 2-3 years. They described the code base of CK2 as twigs and glue. CK3 fixes all of that.
4. Some CK2 expansions will be part of the feature base of CK3 but expanded heavily on (like Way of Life and Holy Fury features) while others are cut completely (Merchant Republics and Nomads), which didn't work out as well as they hoped. One thing I hope they drop is child-rearing stuff, or at least ONLY make it something you need to do IF you decide to - not every damn kid rotting in the dungeon.
5. The earliest time to begin is 867, the Viking Age, but the core events won't begin until 1066. My guess is they'll expand backward in time later on since there's so much interesting stuff in the post-antiquity era; lots of legends and myths from the era: Ragnar, King Arthur, Ogier the Dane, Orlando/Roland, etc... Interesting historical events: Charlemagne, the Gothic Wars, the Lombard Kingdom, the fall of the Eastern Roman Empire and the Persian Empire, etc...
6. The map will be expanded in size to include more of Africa and South East Asia.
7. Character models are being updated, and physical traits carry down in a far more meaningful way - i.e. the Hapsburg chin... Inbreeding will not be kind to the looks of the descendants.
8. Religion is more detailed, more control over traits - and characters can star heresies apparently... which, to me, sounds awesome! I loved forging new religions when upgrading from Pagan to Reformed, but the one flaw is you couldn't change it once it was created.
9. Dynasties will now have cadet branches, which IMO was a big missing part of CK2. These were a big part of medieval history: The Plantagenet House of Anjou and the Capetian House of Anjou were two major cadet branches centered on the same County. There was also the House of York and the House of Lancaster, who were the central dynasties in the War of the Roses, both cadets of the Plantagenet... before the Tudor dynasty (which inherited the claim via Henry Tudor's Lancasterian mother) took it all.
10. CK3 has been in development since 2014 when a few projects, including "Project Titus" were revealed/leaked. As it turns out, Project Titus is CK3. So it's been over 5 years in development.
