For me it would be minecraft.
Why do people like minecraft though, its just a sandbox not an actual game ? Am I right because I saw they bring out a new game for it that might actually include missions for the first time if I read it right and before that it was just a case of build stuff and just an occasional spider but not actual multiplayer competitive games like alot of massively popular games ? I mean the game who wrote this is a billionaire I think
Well, in the vanilla minecraft(no mods) you do have an objective, but that's not the point. You do that just so you can have a few different things and the pleasure of killing the bosses. Other than that, yup, it's just build and craft stuff.
At first I thought tha same thing as you, but the real deal is that mods gave more life to the game. There are "modpacks" that makes tons of changes to the game. It still lacks an objective? Yup, but there are so many things to be made, so much to explore, and it feels nice to make your stuff, specially automated ones.
And yeah, "Notch", the creator of minecraft sold his company, Mojang, to Microsoft for over 10 Billions.
Hard to believe or not, Notch today is a bit sad if not depressive since he no longer works and he can have anything he wants(there's no challenge more in his life).