HARD MODE: Don't say Undertale
I think mine is probably DOOM 2016. I don't know that I've ever had more raw, uncut, can't-believe-how-much-I'm-enjoying-myself FUN than my first time going through that game. I legit was hooting and cackling like a madman while scrambling around blasting demons and dodging fireballs and getting sick glory kills. My first playthrough was roughly 20 hours of some of the purest joy I've ever experienced in my life and I'd give ANYTHING to experience that again.
Honorable Mention: Heaven's Vault. GOD, that game is cool.
i played about 90% of outer wilds close to release, in 2019. just as it was time to put together the Final Run i kind of fell off the way you do when you don't want a game to end
i decided to finish outer wilds a few months later, in August 2020. for my birthday i put together a discord stream where i decided i would finish outer wilds because as a Puzzle Enjoyer it is almost as much fun watching someone solve a puzzie as it is to have solved it yourself. also, as you may have guessed, there was no way for me to actually see my friends or have any sort of IRL birthday gathering of any kind!
anyway, if you've finished that game, you might already know where i'm heading with this (no spoilers!). the Themes and Motifs of outer wilds, ESPECIALLY in the final scene, absolutely fucking wrecked me given that it was, again, August 2020.
I was sitting there with a captive audience of a dozen of my closest friends literally sobbing harder than i ever have at any video game and it was probably The Video Game Moment i'll talk about for the rest of my life

