As the heading suggests, "If you could play a game for the first time again, what will it be?"

I have a few but I would love to play Donkey Kong Country (SNES) for that very first-time feel again. I remember being a young Teenager when it released, playing it on the CRV TV, and two players with my older brother. That first time we saw that Rare logo and the intro of Cranky winding up the music box, and seeing DK come down with the Boom Box, and listening to the game music for that first time was magical. Then selecting that file and watching your progressing and secret unlocks by % on your game file (Before Achievements/Trophies) True nostalgia. I would love to be sitting in that room again to experience the magic of DKC. Games were something else back then.

Honorable Mentions

Zelda: Ocarina of Time - N64

Mario Galaxy - Wii

Resident Evil - PS1

Homeworld - PC

Mario Kart 64 - N64

Final Fantasy: 7 - PC/PS1

World of Warcraft (Vanilla) - PC

Pokémon Blue/Red - GB

Ocarina of Time. The game has so many special, revelatory moments. I don’t know if I’ve ever experienced something as eye-opening in a video game as the moment I first stepped into Hyrule Field and took in its (for the time) vastness.

I played it again recently, and it remains brilliant, but nothing compares to that first play-through.

Final Fantasy 9

Everything was just magical.

Super Mario Odyssey. This and BotW were the two games that tag-team cemented my interest in Nintendo and, more generally, gaming as a whole. (BotW+MK8D+Splatoon 2 kept me occupied from March through July of 2017; SMOdyssey + BotW DLC kept me occupied from October 2017 through January 2018.) Unrivaled experiences!

The original Silent Hill. No question. Didn’t even have to give it a second thought. I will never forget what playing that game for the first time made me feel.

Sure, there are other games I would like to be able to play for the first time again. I could name a few: MGS3, FF7 Remake, RE Code Veronica, RE Remake (GC), Silent Hill 3, Super Mario Galaxy, Mass Effect 2, FFX, Jak and Daxter, God of War 2018, Kingdom Hearts 2, Mortal Kombat 2, Sonic Adventure… and I’m sure there are plenty others. But if I have to pick one, and only one, it’s definitely SH1.

Earthbound
Pokemon red/blue
Final Fantasy 7/9
Kingdom Hearts
Halo CE

Oh man that's hard to decide. My honest answer has to be Batman: Arkham Asylum. I was still on a Batman high after The Dark Knight, so the thought of having a Batman video game with the same voice cast as Batman: The Animated Series had me hyped as hell. I was sold just 5 minutes in. I knew I was in for a special ride. From seeing the interactions between Batman and Joker like it was the 90s animated show again, to using the detective skills, to the psychedelic trip of the Scarecrow level that made you think your game crashed, all being seen through an addicting combat system, stellar music, and an atmosphere that truly made you feel like you were in the Arkham Asylum from the comic books. Everything was just so perfectly made.

What I would give to experience it again for the first time.

Other notable games that also come to mind would be Halo: Combat Evolved, Pokémon Red/Blue, StarCraft, Warcraft 3, WipeOut XL, Vanilla WoW, Half-Life 2, Jet Set Radio Future, and Call of Duty: Modern Warfare (the opening ship level had me feeling like I was watching a Hollywood action movie)

The Witcher 3 is my favourite game ever but I wouldn't want to play it fresh again cause I still get so much out of replays. So...Probably Elden Ring, it's like number 7 in my top list but since the world and exploration makes the game so good and replays are not nearly as good because of this, I'll go with that. 

Chrono Trigger. It do be my goat.

ICO, SotC and Windwaker.

OoT was magical at the time but I would have to forget all the Zelda games after it as well.
Same for BotW, would have to forget about TotK to be able to enjoy it fresh.
Windwaker stands on its own and feels timeless, like ICO and SotC.

If you mean go back in time and experience the game again fresh in the same time frame,
Half-Life, Oot, MGS, Baldur's Gate, Grim Fandango, basically relive 1998!
I was also 24 at the time, lived in a cheap place, landed a good job 2 years prior with a lot of disposable income, had cutting edge surround sound for the time, a CRT projector, and was playing on a $5K PC with 19" trinitron monitor. Thus playing OoT and MGS projected on a 72" screen with surround sound and the others at 1280x1024 @ 100hz.