Why is a game about being a delivery boy so good? Is it the infrastructure building mechanic? Is it the batshit insane storyline? Is it the fact that every mountain is climbable? Is it the reserved use of combat and massive punishments for killing people?
Who knows, all I can say is I haven't had this much fun with a game in ages.
It was like Kojima wanted to make a game about forming bonds with other players and not one about killing (especially because killing someone means you have to spend 3 hours trecking up the mountain to an incinerator to burn their body before they go nuclear).