Well here are the games that mean the most to me personally, in chronological order:
Donkey Kong
My first console was the Coleco Vision. Back in those days my family and neighborhood were tighter and I was a kid. My dad and uncles were able to "get stuff" and "know people" and "find things," if you know what I mean. I mean we are working class people but they made do, you know? So I they got me a Coleco Vision but there was no box or instructions, hah hah. And Donkey Kong was the first game we got on it and it was big deal having a video game in your actual home! So the parents and grandparents watched us play and joined it, it was so cool. I don't even know like if it was the original Donkey Kong, I dunno, I just remember there were three levels. The first one is the classic running up ladders. And there was one with like a bunch of elevators. This is all I remember.
Street Fighter 2
8 characters?! Each with different styles and moves? I can't even explain how much this blew our minds.
This game was not just a game, it was a focal point of my social life as a child and young teen. I never even got good at it, it was just where we would gather, and have something to talk about. Half the boys I knew were into basketball, and the other half were obsessed with Street Fighter 2, and these were the cultural touch points with which we connected.
The Legend of Zelda: A Link To the Past
Obsessed. OBSESSED.
A family friend/neighbor I grew up with knocked on our door. She is a couple of years younger than me. She is holding this cartridge in her hand and is asking for my help to figure out a part in her game. We load it up on my SNES and it's this Zelda game- I had played a bit of the NES one at a friend's house I vaguely remember but I didn't really think much about it. Where she's stuck in this SNES sequel is that there is a book on a shelf, but of course there's not jump or climb in this game. How do we get the book? So I'm just messing around and eventually I discover that Link can run-charge at things and it knocks the book down.
Well... of course I wanted to see where this goes. And thus the world of true exploration in games is revealed to me. When I am able to get my own copy I end up playing and replaying this game obsessively. I would end up replaying it as a way to comfort myself during the more turbulent teenage years. I would come home from college on winter break and do a "speed run" style replay while helping my sister deal with her teenage years.
Assassins Creed 2
I did not really play video games much from the ages of 17 to 30. I mean sure I played a bit, but it is occasional and social. Guitar Hero etc. Final Fantasy 8 was the one game I actually played played during a bout of post-break-up depression but other than that I was just into other stuff. So all big games that now dominate nostalgia from the N64/PS1&2 era just passed me by. Baldur's Gate, Ocarina of Time, FF7, Half Life... nope, never played them. I watched someone play half of Resident Evil? That kind of thing.
Then I'm in my 30's and PS3's are cheaper so what the heck I need a DVD player anyway. I don't even remember how/why I got my hands on AC2 but damn if it didn't blow me the hell away. Renaissance Italy! A movie like story! Crazy conspiracy theories! I was enraptured- this is what video games are now?! AC2 basically pulled me back into video games as a central focus of entertainment the way they were when I was a kid.
The Witcher 3
Obsessed. OBSESSED.
This game basically is my adult version of A Link to the Past. Exploration, world-building, and the satisfaction of knowing where everything is.
Bloodborne
The game that got me into this whole FromSoftware business that defines the limits of my patience with difficulty and sets the standard for my favorite type of games- 3rd person melee combat. Subreddits, discords, cheese tactics, min/maxing builds, speedruns, challenge runs- I know about all this stuff because Bloodborne got me into Dark Souls and then I'm all-in.