Eagerly waiting for the end of Ten Desires analysis. The introduction of Legend of the Great Gods is pretty much unlike anything I ever heard from ZUN before and I really don't know what to think about that one. It surprised me the first time I heard it and still sounds very strange whenever I reach Futo.
Regarding Futatsuiwa from Sado, what I find immediately apparent is how danceable and fun (in a, say, Bluegrass sense) that theme is. When you get to the extra bosses, they are usually interested on terrorizing (Flandre), awing (Ran and Yukari), unsettling (Koishi or Nue) or saddening (Mokou) you. Suwako is obviously happy in her theme, but she's just a bit too frantic. Mamizou instead throws some kind of youkai hillbilly dance at you. What a culture shock.