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 opens up new possibilities as the challenges get harder, and it's all but necessary for later mountain areas.