Final Fantasy 7 (the original).

And it's not even close. What a journey.

Dark Souls.

But I suck and this time I don't get sucked into the entire series. That oughta save me some time and money.

If I had to take a Retro game, Chrono Trigger for sure.

Mass Effect trilogy.

Or maybe Bioshock.

Either/both.

Very late edit: Deus Ex. I still play it every once in a while and while the graphics are terrible, it's a lot better with GMDX and you get used to it very quickly. That game is still a masterpiece.

There are two games I would love to play for the first time again and those are Portal and Dishonored.

Portal is obvious - it's a well-refined and immersive puzzle game with enough story and atmosphere to keep you invested, but never so much as to pull you away from its puzzles. It may only be a short game, but it is one of the best!
The only people I know who haven't given this game the upmost praise are those who've never played it before.

Edit: Portal 2 is also a fantastic game, but it definitely leans on the story more. That is by no means a bad thing though, as we wouldn't the absolute menace that is Cave Johnson without it.

As for Dishonored, the original is Arkane Studio's best game IMO - the world it's set in is so interesting and brimming with lore; the levels are well crafted, and reward the player's creativity and exploration without ever feeling forced; The gameplay is challenging, but without ever feeling overwhelming. I'm sure it has it's flaws, but all these years later, I still remember how much it got right.

Edit: Dishonored 2 was very much like it, and I remember it for all the same reasons, but the first is the one that really captured that lightning in a bottle for me.

I also loved Prey. It plays in a similar style without feeling too much like it's predecessor. I can't say I liked the Roguelike DLC very much though.

Edit 2 Electric-Boogaloo: I keep forgetting Dishonored uses the American spelling. I always remember it in the British spelling. Oops.

Earthbound. Even on my subsequent yearly-ish playthroughs, it's so easy to get immersed into the beautiful quirkiness of the world.

Gothic

My first open world game, unmatched freedom to do what you want and to go where you want, exploration rewarding with handplaced loot everywhere. I lived in that game for a whole year.

Probably Planescape: Torment

Factorio of course, because that's what people already do. They start over and over again with ever bigger plans.

Easily Majora’s Mask

Edit: upon further speculation, Final Fantasy X is tied

I wish I could experience Portal for the first time again.

Half Life or Command & Conquer for me

Freelancer

System Shock 2 or Thief: Dark Project. Those two were the games that impressed me most in my 40 years of playing games.

Honourable mention: Minecraft. The first few weeks playing that come very close.

Definitely Subnautica in VR. I didn't play it on flatscreen, only in VR, and it was the most immersive and amazing experience out of any game.

Doki Doki Literature Club. Because I got spoiled the first time I played it.

Either:

1. Mario 64 - seeing a fully realised 3d world for the first time was mind blowing. Great music, adventure, and fun.

Or

2. Morrowind - what a wild and rich world to explore for the first time. My best friend and I rotated shifts for weeks during school holidays. Great memories.

Baldur's Gate 2. Would love to re-live the feeling of wonder and suspense this game offered, although it'd probably help to forget about modern RPGs too, to keep with the nostalgia.

Monkey Island 2: lechuck's revenge.

Probably Red Dead Redemption. It was an amazing game and even fun to 100%. The soundtrack was the icing on the cake.

Half-life is close too. That game blew my mind as a kid.

Neverwinter Nights

Everquest. No other game I've played before or after instilled that feeling of exploration and wonder that this game did. I'm so glad I got to experience that before I got older.

Super Metroid

Either Oblivion or Fable: The Lost Chapters

The first Mass Effect. That moment when Sovereign speaks... instant goosebumps. ("Rudimentary creatures of blood and flesh, you touch my mind, fumbling in ignorance, incapable of understanding.") This also presupposes that I haven't played the other parts as well of course. I actually played the second one before the first one back in the day.

Brothers: A Tale of Two Sons

Inside

BioShock

All great stories with some very powerful moments.

Super Mario Galaxy

Final Fantasy 6

Super Mario 64

Super Mario World

Resident Evil

VVVVVV

Factorio

There's a couple I'd have to choose from on this:

Portal 1 and 2 (if it can only be one game and not the series then portal 2),

Legend of Zelda Tears of the Kingdom or Breath of the wild maybe,

Prey,

Firewatch,

Fallout: New Vegas,

FRACT OSC,

Donut County,

... This may have been more a list of my favorite games rather than play for the first time again...

Minecraft, botw

Death Stranding

I still have dreams about that masterpiece of a game. There's just so few like it.

Champions of Norrath on PS2. I played through the entire game with my dad and it was the most fun I ever him.my mother said he used to play video games all the time, but then stopped (having kids probably does this to many). So when he said he’d play the game with me i was very excited. i only wish i could have found the games sequel, return to arms, before heading off to college. that would have been a summer to remember.

i don’t know why he never shared his love of video games with either me or my sisters. some dads are weird like that. i bought him a series s for the holidays and while i don’t think he plays it, he enjoys watching his grandkids play.

CrossCode

Roller Coaster Tycoon, 2 preferably. Like, if OpenRCT2 could magically time travel back and exist on 12 year old me's computer, it would be bliss.