I agree with Brother Mark in that Maddies are schweeter, have more cocoa flavors, probably more earthy flavors and are a rounder, richer smoke but IMO definitely not stronger.
A maduro wrapper is made by fermenting the leaf longer and at higher temperatures in the bales. Some manufacturers actually cook the leaves in a pot to make maduro wrappers. At the higher temps and longer fermentation the nicotine level naturally decreases and more of the sugars in the leaf are brought out. Maduro wrappers are definitely sweeter in flavor and don't have the same level of spice and kick as their natural counterparts. Just my $0.02
Aloha,
Wade