(Saw this question asked on another popular link aggregation website and it got me thinking)
If you could play one game for the first time all over again, what would you choose? This might be because you want to do it all again, or because you don't think you got enough out of it the first time. It could be experiencing the game exactly as you were back then, or experiencing a game with what you know now.
For me, it's Legend of Zelda: A Link To The Past, experienced exactly as I was back in 1991.
Nothing comes close to how jaw-droppingly amazed I was by that opening sequence. The epic orchestral score, the cinematic rainstorm, creeping around in the dark... it was a generational leap above anything I'd played on 8-bit computers and consoles, and even the Megadrive. I'd love to play it again without thirty plus years of Nintendo/Zelda knowledge, or without knowing about the dark world.
World of Warcraft. Starting out in an MMO for the first time is magical. No worries about the endgame, just the desire to explore and learn.
I responded to another comment here about it. WoW and other MMOs would be my choice -- but to make it any fun you'd have to rewind the whole world. Not only get rid of wowhead, wowwiki, raider.io etc., but get people to forget they ever existed, forget how to do data mining so effectively. Also get rid of streaming and video sharing services so that you had the chance of discovering things on your own. You wouldn't be the first, but you wouldn't know that.
Yeah, the internet ruined online gaming.
Oh yeah, WoW hands down. The sense of wonder as I explored the world the first time was incomparable to any other game.