>>712508828 (OP)
Return to roughly gen 3 era art direction.
Not open world. Remains 3D with a controllable camera, but uses well designed routes and caves with detailed environments. Battles and catching can still happen in the overworld, PLA style.
Retain some open exploration similar to kanto, letting you do some gyms out of order. Have the gyms scale by badge.
HMs return, but pokemon compatible with the HM can use it without learning it. Alternatively, you still have to learn it, but the HMs are actually usable in battle and can be forgotten without a move deleter.
There are no friend characters. Your rival is also the main antagonist. He aims to make the pokemon league go defunct. Either because he's a scorned ex-gym challenger/leader/champion, or because he's seen how gym leaders and champions in most other regions do jack shit when their respective regions are in danger.
Smaller dex, allowing for rideable pokemon, like in LGPE.
Tweak idle animations in battle so that the majority of pokemon don't look like they're just standing around.
Includes side activities such as the game corner (just use a different minigame slots suck ass anyway), secret bases, amie, gimmicky post-game towers, things like that.
Dumps IVs. Literally just get rid of them. They've already defeated the intention of IVs by letting you change them outright so just skip the middle man and get rid of them.
Implement an expert mode, making set mode and doubles the standard, and prevents you from using items during trainer battles.
Keep the exp share, but tweak the exp given or at least the levels of everything. On that note, cool it with the level up learnsets. Unironically too many pokemon have too much access to too much coverage. Keep it to TMs if you must.
Cool it with the free items as well. Just running around in SV will net you more potions and items than you'll ever use.
Send Gamefreak to hell and blacklist Ohmori from the industry
Or something like that
