Give me ideas for a basic and fun game

Hello there mate,

Hmmmm I think the first stepping stone should be the foundation of your game: what's the main thing that people will do in it.
Since you want it basic, let's stick with what i believe the canvas for many indie, successful games -->Platforming-Puzzle
I could also recommend giving it rogue style elements,to "up" it's replayability and keep people coming.

In order to make it more fun, I think you should achieve this through the vibes and style.

Some games that are fun and basic in my mind is Binding of Isaac,Slay the spire,Enter the gungeon,Hollow knight and A Hat in Time.
Checking out other games and getting inspiration should be you go-to priority.Just see what you can do better.

P.S.I have an idea for a game but i don't think it is much basic and it's gonna be length-y.I am willing to share it with you if you want.DM if you do.