The FO4 / FO76 settlement scheme. I want to be able to break into a junkyard, stuff 200 pounds of trash into my jeans pocket, and then return home to fortify my backyard.
Mechanically speaking, a few things: loading and storing, quick travel, respawning, cheat codes, bullet time on demand, personal inventories, and monitoring and improving my own metrics via a user interface.
GTA: San Andreas cheats allow for some wild antics. Picture this: doing a quirky macarena while cycling through my inventory, and then ending up perfectly healthy, equipped with body armor, holding $250,000… and an RPG-7.