I don't know why you chose Risk as an example anyway since it's mostly determined by luck.
From: Paratroopa1 | #006
I'm not sure how you decided Settlers of Catan meets three of his four requirements, given that it doesn't meet any of them. Randomness is heavy, games are long, there are turns, and the game can be scaled up but it's difficult.
Having turns shouldn't be a deal-breaker. After all, it's a game of diplomacy, right? So there's always something to do even outside your turn. Truthfully, that condition is meaningless anyway.
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"As the size of an explosion increases, the number of social situations it is incapable of solving approaches zero." -Vaarsuvius, Order of the Stick