What does Blackmoor have that Mystara doesn't?

[aldarron]

For me it's both nostalgia and a love for the origins of the game.

Ditto that. And I'm drawn to the rugged northern landscape, the mystery of the place, that sort of thing.

Mystara feels more settled and defined, more mundane in a sense, but of course that depends a lot on where you are in the world.