I'd probably go with Minecraft, oddly enough. Sure, it wasn't the best thing out there and it had its ups and downs, but when it comes to *Game of the Decade* nothing really gets as iconic, well known and influential as MC.
Red Dead Redemption 2 for me.
The world is so immersive and the voice acting of all the npc characters are amazing.
So much to do in that game, I've never had that much fun with a game in my life besides witcher 3.