But if I were forced to pick...
I think I'd have to go with
Shadow of the Colossus. Just the
experiences of meeting those colossi, the epic battles, the slow subtle progressions, exploring that pristine, abandoned world... that's a game that leans heavily on how you experience it, so it would really benefit getting to go in blind all over again. Other "Experience" games like
ICO,
Journey, and others in those veins would be good.
I think
Breath of the Wild would be a strong contender. Rarely has a game kept me entranced so consistently throughout with all the exploring and adventuring. I love a lot of games, but BotW was the first that came to mind where the moment-to-moment experience of it was so consistently new and inspiring.
Story-heavy games like
Ace Attorney and puzzle games like
Baba is You would also be good to experience for the first time again, of course.
Baba in particular had some mind-blowing moments of discovery that were fantastic... but that one in particular is so hard that I wouldn't get very far anyway.
I actually don't think I'd like to do any of the
Souls games. My first playthroughs are, while still gripping and rewarding, often also stressful and difficult and frustrating. There are fantastic moments in each game that would be fun to re-encounter for the first time, and re-exploring the environments and re-discovering secrets would be great too, don't get me wrong. But I think some of my best memories of each game come on replays as I'm less stressed since I'm already relatively good at the game, and I'm just getting to mess around, experiment with builds, etc.