As someone who never played the games as a kid, I can be more or less impartial in saying that Mario Bros. was probably the gaming industry's big break.

Guild Wars (the original) Just so nostalgic to me. Gameplay is fun even after all these years.

Maniac Mansion or Zack McKraken on the Commadore64. At the time...at that age... we were living in the future, and it was amazing.

Gothic 2.

earthbound. my first RPG that I understood, plus SNES is GOAT.

Dark Souls remastered taught me how to look at life differently. I now accept failure as part of the process of growing, not something that should be avoided at all costs.

Also it taught me how to parry like a G.

Command and conquer generals zero hour

Marathon, by Bungie. From the box it came in, to the hugeness of the spaceship, the coolness of the story, all the secrets, and the fan community that sprang up to research and theorize.

And then they made it open source so anybody could play it on any computer.

It's not favorite game to play any more, but it was the greatest game to me.

Ocarina of time. All Zelda games since are to some degree compared to it in terms of how successful it is monetarily, gameplay and story-wise. So many modern adventure games are based on this one game. It’s the game that finally made target tracking in 3D work. It’s so well thought out, that a blind streamer is able to play the game probably better than I ever will. If most common people know of “zelda” it’s because of this game. There are so many memes from Zelda in general. It’s one of the few games from my childhood that I will replay for the rest of my life.

ET for Atari, classic.

Ultima IV. All the JRPG stuff started here.

Final Fantasy 1 - It wasn’t the first RPG, but it pretty much defined the series. It still has tons of playability, I revisit it more or less every 5 years. I still have yet to beat Warmech, and only have encountered him a handful of times.

But most of all, it’s the game that saved Squaresoft. If it had failed, we would have missed out on so many great games, including ones also mentioned in this post.

Runners up have to be Donkey Kong, which brought us Mario, which in turn restored vitality into the at home console game industry, and Double Dragon, which brought us PVP and Co-op combat.

Honorable mention would have to be that Simpsons arcade game where Marge can fight with the vacuum cleaner and TMNT 2 - Two classic, very difficult, drain your change jar games. I’d throw Mega man 2 into that mix as well.

Just cause three. blow shit up, kill bad guys, just enough story to explain it all. even better, it strikes a good balance of minimal story and compelling story, which a lot of games like that kinda suck at.

Not a single game but a series. Legacy of Kain is still my absolute favorite not because of replay ability or anything like that but because of the story.

Quake 1.

The game is kinda meh, but the modability spawned an endless amount of awesome stuff to this day. Even Half-life is basically just a Quake mod.