I feel like people obsess over Dark Sky because it would have slotted almost unchanged into some hypothetical post-Mac OS 9 design language if "lickable" OS X had never existed. Or, if you prefer, Dark Sky embodied the engineered simplicity and power that made people so loyal to the earliest Apple GUI software in favor of the more, uh, ebullient character that has driven the last 20 years of Apple UI design (sic). Note that I still put Apple's UI design well ahead of both Android and Microsoft, but it has regressed substantially.