What I like about BP shooting:
First, they are, arguably, the most beautiful firearms ever made. They fit very nicely in your hand.
Real BP is just plane filthy and there is no getting around it. The cap and ball guns I have belch out smoke and sometimes sparks fly out up to 10 feet.
If you cast your own shot it costs very little to shoot all day. You can adjust the powder charge from "POP" to "KA-BLAM"!
What I don't like:
Real BP deflagrates and produces sulfuric acid residue. The entire gun has to be detail stripped after firing and thoroughly cleaned, greased (and there is a trick to that) and reassembled. Every single time.