What's the Appeal of Shell Cordovan?

As a newcomer to the world of fine shoes, I have read with interest numerous threads discussing different shoe styles, brands, construction methods, and leathers. Shell cordovan comes up a lot and is spoken of in reverential tones. What exactly is its appeal? Is it appearance? How is this better than found in a well-polished calfskin shoe? Is it its greater toughness? Durability? Resistance to scuffing? Or is some of its appeal simply its relative rarity?

Vancouver