For the last 2 years I've hunted squirrels with ML only. Using a .32 Crockett and a .56 smooth Renegade with shot.
Except for archery season with my recurve, I've only used ML rifles for deer the past 2 years also. Had success with both my GPRs, a .54 flint and a .50 percussion. I don't see me ever going back to the shotgun.
I still tote a modern shotgun for birds and ducks, but at least it's a SxS double. I may switch to ML only for that someday too, just to bug my buddies.
There's just a really big "cool factor" that goes with traditional muzzleloaders. Not so much the extra challenge, altho that is a part of it too. It's just more fun with a ML. I don't NEED to kill something every time I go hunting. And I like the smell of burning Goex.
ML season gives me an extra weekend of deer hunting and that is why I got started with muzzleloading in the first place. Woods time is the important thing about hunting for me. I buy extra deer tags every year and let lots of deer walk every year just to make sure I get to hunt as much as is legal. Once I figgered out how much fun I'd been missin' by not shooting blackpowder, I wished I'd started sooner.