Deluxe Galaga
Datastorm
Cybernetix
Pang
Those aren't exactly "easy" games, but they are simple to pick-up and play for quick gaming sessions and are very good games. (Well, though if you eventually get GOOD at them, a game may last for a while )
I'd recommend my own games, though some people think they aren't very good, hehe
https://ralizasoftware.neocities.org/amiga.html
Quasarius is very simple and very easy too
IK+ is also great for quick sessions... you need some time to learn all controls, but you can have some fun just smashing the button and pushing on random directions up until you learn all moves
Shuffle Puck Cafe is also another good option, and you can pick easier opponents all the day if you want so.