I'd go back and build on some of my favorite games that developers have ignored for one reason or another.
An NES Zelda style game but with improved graphics and more importantly a world builder (like Minecraft) so that you could play the game over and over again.
A Final Fantasy Tactics style game that also included exploration, dungeons and quests like a normal RPG.
A Guitar Hero style game where the rock songs were made into a musical, so you'd see a story play out while you played through the songs.
A Katamari game that had the basic gameplay and a great focused soundtrack like the original, but actually make it a full length game. The original game was perfect except it was way too short.
curl-6 bet me that PS5 + X|S sales would reach 56m before year end 2023 and he was right.
My Bet With curl-6
My Threads:
Master Thread, Game of the Year/Decade
Switch Will Be #1 All Time
Zelda Will Outsell Mario (Achieved)
How Much Will MH Rise sell?
My Bet With Metallox