There are many games that I loved and would enjoy playing for the first time, but I'm going to pick Mario and Luigi Superstar Saga. My reason being that I spent the vast majority of the game waiting for it to morph into a spiritual successor of Super Mario RPG back when I first played it, rather than giving it a chance to stand on its own as a unique and hilarious game. My preconceived idea of what I hoped the game would be really hurt my initial enjoyment of it.

For a runner up, I'll mention Kirby's Dream Land 3. In the days of Blockbuster rentals, I'd rented Kirby Super Star first, so it took me a while to get used to the more traditional Kirby powerup system where copied abilities only do one type of action each.

Learning Team Fortress 2 for the first time as a teenager was such a crazy fun experience.

ICO

such an amazing game that never seems to get any love

Minecraft, specifically Beta 1.7.3.

Monkey Island or Little Big Adventure

Nier Automata

A game I will never forget

Final Fantasy 7 or 9, Earthbound, Secret of Mana, Phantasy Star Online

Skyrim. After 200 hours, you start becoming really aware of the "seams" and the clunkiness of the Creation Engine. Although, while you're still working your way through the quests, and every stat isn't at 100 yet, it's pure pure pure bliss. To have that original feeling back. Gah!

StarCraft's campaign was a masterpiece. I get to include Brood War here too.

Shadow of the Colossus and some Silent Hill stuff

Spyro the Dragon as I was back in the day. That game has always been so magical for me.

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.

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.

Hotel Dusk.

Bioshock. I am sure you can just replay it. The twist at the end... I wish I could relive the surprise again.

Probably Fallout New Vegas (if that even counts as retro yet). I've played it to death ever since it came out and can't even remember the first time I completed it.

Ghost Trick: Phantom Detective

The story has so many great twists and turns even up to the very end. There was a distinct point about 75% of the way through when I came to the realization that I had to binge the rest of game. Even if it meant I got zero sleep that night, I had to see how it ended.

It was so good I wish I could experience it again blind.

I have seen no mention of Planescape Torment, so there you go.

If I were to experience it as I am today (and judge it versus games with modern graphics etc), I'd pick Ori and the Will of the Wisps. It quickly became one of my all-time favourite games, and I finished it three times in a year when I discovered it. Beautiful in so many ways.

Half-Life is probably the game that has had the biggest impact on me, though, so that would be my pick if I experienced it as I did around 1998.

Half-Life 2 and Shining in the Darkness.

Morrowind but it wouldn't matter because I don't have enough time to get immersed in it anymore.

Read dead redemption 1. A masterpiece.

Space Invaders

Asteroids

Pitfall