I don't really like the free fight missions. I can't get hit once? What's the point in that? It makes more sense as a special assassination mission type (there IS one like that). Just make them convenient "kill enemies here without having to sign up" locations, not annoying challenges that never go away.
But still, getting enemies into a bunch and swinging the Wiimote to slice off about ten heads at once, while coins and blood cover the screen, is intensely satisfying.