Setting
>3D Big open world like BotW.
>dense forests, arid deserts, wide oceans and lakes, dark caves and huge mountains as well as well as sprawling cities and quaint villages and towns
Story
>less emphasis on fighting the evil team and saving the world, more emphasis on exploration, discovering secrets.
Gameplay
>at least 150 new pokemon
>fully customizable characters height weight, etc
>can climb most believable surfaces like BotW
>pokemon are seen in the overworld and fill the world believably.
>they have unique characteristics in how they act and feel like actual wild animals
>bird pokemon flying in the sky, schools of fish pokemon, a lone snorlax sleeping by a lake or eating from a berry bush.a ursaring might attack you, defending it's teddiursa cubs if you get too close.
>your character now has a health bar. you can be attacked by wild pokemon while out exploring. "dying" is the same as if you ran out of usable pokemon.
>18 gyms one for each type. must collect all badges to advance to elite 4.
>gyms can be beaten in any order, their team is always the level of your highest pokemon
>elite 4 are not based on type, but around team synergy
>beating the elite 4 allows entry into pokemon world tournament filled with the toughest trainers from the past and present
>IVs and HVs are implemented in a way that is more fun, and natural because they are mandatory if you want to stand a chance against later trainers.
>No more having to spam potions or revives. battles are won by strategy and skill
Battling
>battles are now real semi real time
>3d isometric view during battles, variable sized playing area with obstacles based on where the battle is taking place.
>pokemon are controllable for a set time each turn, based on their speed stat
>can hide behind trees, rocks to block some attacks
>some attacks can break through obstacles and effect the battlefield in other ways such as setting a certain area ablaze, or flooding an area to boost the power of water moves.
etc