These could be games that left a lasting impression on you, games that had stellar gameplay mechanics, characters that captivated you, games that you played tons of hours on, etc.
I wasn't able to start gaming until I was around like 12, but when I did, I loved a game called Dungeon Defenders on the Xbox 360. Came out in 2011, so it's not nearly as old as most of the games listed here.
Dungeon Defenders was actually full of modded accounts on the Xbox, and they distributed loot everywhere that did like a billion damage and one shot everything (yet somehow I still sucked at the harder maps lol). I could never enjoy the game now with all the modded shit, but back then it was fucking awesome. It's the game that got me into modding and is the reason I'm as computer savvy as I am today, so it will always be a fond memory in my head.