You can create the world, backstories,
religions, economies, countries you can visit
which have different ecosystems, and a map for the world basically a living and breathing world even without you the world is still going, for example, you are in the stone age and sleep for millions of years and when you wake up there's flying cars, there's the history you haven't heard of, wars, etc. In the world, you can save it and play as different characters in it who each have different goals that they want to achieve and personalities. Once one character achieves their goals you can switch to another because some people like me have a good world that they don't want to leave just because they did everything they wanted to do with that character. Also one character you play as can another in the other in the world. You can also meet up with other characters you played as in the world and team up or who knows anything!
I hope no one has the same idea as me lol