What one game would you keep if you're stuck all alone on an island?

[Bloo]

Well, this question was asked on another forum I browse, so why not ask it here?

So you are trapped all alone on an island, and you can choose only one (1) game to play, probably for the rest of your life.

here are the rules for you :

• You only have limited internet access, a narrow bandwidth perhaps.
  
• Therefore you cannot play in online games like MMOs.
  
• But you can dowload, very slowly (but time is on your side) mods.
  
• There are no hardware restrictions, so the PC can be as powerful as you want and runs any OS you wish.
  
• The game can come with its expansions (if any).
  
• But you cannot choose more than one version of the same game, like for example, you can only have Max Payne 2, but not the original.

What would you choose, and why?