I think an interesting way to define the greatest game of all time would be a game that captures your attention the longest and provides the largest variety of ways to play.
To that end, I would say StarCraft 1.
My personal reasoning is I love games that have user generated content to keep you coming back to enjoy fresh experiences. StarCraft 1 had a game mode called use map settings where you could play maps made using the built-in level editor. There was enough complexity in the level editor that basically the sky was the limit.
You want to play a tower defense? StarCraft 1. You want to play an RPG? Which franchise do you want to play, cause a lot of them are on StarCraft 1. You want to play an action adventure game? StarCraft 1. The list goes on lol
I’ve never personally played it, but I feel like another example of this would be Roblox and another one that I have would be Gary’s mod.
Fuck I had to stop watching after the bit with his dog. That’s heartbreaking