All pokemon that don't have split evolutions can now evolve by Levelling up, but it's deliberately high for pokemon with specific conditions (i.e. 60 or 70).
Similarly, Pokemon with +41 level requirements now get new alternate methods of evolution they can access at lower levels, unless they are Pseudos (looking at you, Gen 5)
Item PC is brought back, seriously what the fuck GF.
"Battle Effects: Off" option now cuts out more animations such as releasing, calling for help, etc.
Lots of items are now removed and their effects are now consolidated into pre-existing items.
E.g. Mystic Water is removed and Water Stone gets its passive effects making it both a use AND a hold item at the same time. Magmar needs to be traded whilst holding a Fire Stone to get Magmortar, and so on.
Arceus Plates, Tapes and Multi-Attack memories are removed and Z-Crystals now perform their functions.
Oval stone and Lucky Punch are removed and Lucky Egg now gets their effects.
Megastones are removed and replaced with an item that's just called "Megastone", it can only be used once per battle anyway, seriously why.
Toxic Orb is removed and Black Sludge gets its effect in addition to healing poison types.
Deep Sea Scale and Deep Sea Tooth are now just Deep Sea Relic and so on.
etc. etc. etc. Lots of cases of the in-game items being redundant so roll them into other things. Battle items/Berries should stay single-purpose for balance purposes.
Bottom screen should always show your party formation and allow you to change it, as well as Save being available at all times. These are the most commonly accessed menu items. Seriously, you can move the Rotom map to the side and have room.
Menu now opens your Bag immediately, and other menu items can be accessed from that screen.
Can access Pokedex from pokemon status screen and PC box.