Trying to list games for the systems I have played significant amount of time on.
NES - Super Mario Bros 3 , could just as easy pick the first Super Mario, but SMB3 is the first game ever I remember liking
SNES - Super Metroid , this is kind of weird since I have not played that game or even like the series. And I think more of JRPGs is the genre that defines the SNES, but somehow Super Metroid is the first game that comes to mind when I think of the system.
N64 - Super Mario 64
GC - Super Smash Bros Melee
Wii - Wii Sports
Wii U - Super Mario Maker, the only game where I found the gamepad thingy nice to have.
Switch - Nothing comes to mind, my view of the switch is more general than specialized so no one game define it for me
PS1 - Crash Bandicoot
PS2 - Kingdom Hearts
PS3 - Uncharted 2 Among thieves , or just any game from Naughty Dog
PS5 - Nothing stands out as defining so far
Dreamcast - Shenmue
PC - Counter Strike, another game I have not played that much or even like. But online FPS games is just PC for me
Game Boy - Tetris
Game Boy Color - Pokemon Gold/Silver/Crystal
GBA - Fire Emblem, I bought a modded GBA just to be able to play this game in a modern way
DS - Warioware touched
3DS - Nothing comes to mind, did not really like the system or the games on it that much