Although if mods are included, that would make Skyrim like over ten thousand hours of content, easy...Super Smash Bros Melee, because it is the best game ever.
Unless I can use mods on Brawl, because then I got Project M, Brawl Minus, Project 64 eventually...
By that logic, Doom 2 is the obvious choice since it has more mods than any other game in existence. Thus, the obvious choice. *poofs*Although if mods are included, that would make Skyrim like over ten thousand hours of content, easy...
So Skyrim