At least Nathan Fillion hasn't been typecast. I still watch Castle for the humor but I think the writers of the show are struggling to make a proper ongoing storyline after Rick and Kate got married.

I saw Nathan on "Two Guys and a Girl". I think his characters Johnny wrote a small poem about his wife, Sharon.

Johnny: I look back at my life, and think about my hot wife.(Reading off a piece of paper)
Sharon: Go on. (Smiles)
Johnny: That's it. (Shows her the paper)

Buffy was a classic. It was a horror/comedy genre that had never been done before.