The original Madness is the red bottle has a big BIG, almost scary peppercorn opening and eventually settles into a floral and a very nice floral at that, sweet at first but then less so as the sandalwood kicks in.
Natural Black minimizes the pepper in the opening (and I have read that it is black pepper not the pink pepper as in regular Madness), skips the sweetness and is a very woody floral. The woods in the base are different and brighter. I haven't read it but my guess is cedar. Very unisex
At first I preferred Red bottle, but now I think I like NB better.