RetroGaming

Quake 3 Arena. Or more specifically OpenArena + baseq3 and other mods like ratmod. Most fun I have had playing a game ever.

I agree with lots of what's already been said and haven't got much to add to those extant conversations, so let me try to add in some that I've not seen:

RuneScape is a candidate. I started way back with RS Classic (the sprite-based one!).

Oh, and Dwarf Fortress too. That began in 2009.

Achaea and/or Lusternia are way up there but I don't imagine anyone but me can share the experience.

Oh, as well, Mount & Blade: Warband. Quite the adventure(s).

I don't really game anymore. But this thread did dredge up some memories, old and new.

Thank you.

Space Invaders

Asteroids

Pitfall

I know this is almost a stereotypical answer, but the Witcher 3. because after that game i went and read through all the books. so if i got to re experience it would be the difference of finding siri after 100 hours of gameplay and finding siri after 5000 hours of story. "find siri' is Geralt's primary motivation throughout the books. i can only imagine how satisfying and emotional that scene would feel for the first time with the weight of the books behind it.

I think this is a tie between Bloodborne and Panzer Dragoon Saga. Absolute masterpieces, both. I replay both of them at least once a year, but it would be wonderful to go back in fresh.

Star Control 2

For retro games my answer is probably Yoshi's Island. If you include modern games I'd likely go with Hollow Knight. If VNs count then Echo.

The Binding of Isaac.

This is the eternal game of ever. It is balanced, fair, excellent feedback (time to win), super I'm depth unlocks, one of the best meta games. Take the time to learn the basics and this game is infinite.

The end of the game blew my mind out of the water in a way no other twist has ever quite captured. It might have been the mental space I was in at the time too. Whatever the case, I will always remember the first time I played it.

I also wish I had played the first Golden Sun before the second, so if I could put a duology and that caveat in there? Definitely those two.

I'm gonna say Skies of Arcadia, just love that game, and it saddens me to this day that Sega have abandoned it.

Breath of the Wild or Tears of the Kingdom. BOTW was my first Zelda game and I honestly loved it. I would sit for hours in the living room zoned in to the game with checklist paper and notebooks next to me to keep track of what I was doing. If I could do it again I'd instead use an interactive map like I did with TOTK.

As for TOTK, the Rito dungeon was my favorite and if I could experience that adrenaline pumping battle for the first time again, I would. Tulin is a baby and I love him.