Great work! You can really see which areas of the country have large black populations.
Minority in general, really, or at least minorities who vote regularly. A lot of Hispanic and Native American counties swung as much as the heavily or significantly black counties in the South.
Ohio is a bit of a sore thumb, but I'd say upstate New York is the biggest sore thumb for not being easily explained by demographics (the minority counties), economics (at least we know central Ohio has a thriving economy, so its pro-incumbent swing is not that odd) or Sandy (New Jersey and NYC).