I'd pretty much like to re-experience any game I've ever loved for the first time, but for the sake of narrowing it, if I could have Red Dead Redemption or The Last of Us and a Neuralyzer, I could die happy. Almost equally I would like to get every part of Skyrim just the way I like it with mods, like I have it now, and then forget I had ever seen any of it for my first play-through. And right behind that, is Mass Effect.
Those are what I feel like I would most love now, as my current self, to experience again like they were new; but that answer is different from what I would want to re-experience as though I were a child again like when I first played Final Fantasy 7 or Metal Gear Solid. Going to a time when the very idea of games with story and some scope was new to me is a different proposition.