"I don't think Dick Van Dyke sounds like good casting for Harold Hill. I don't think I'd believe him as a lying conman. I think he's just too nice seeming. I know acting can be surprising, but given his persona, I doubt the casting would work for me."
Interesting, because one can look it it from the polar opposite perspective. For a con man to be successful, it's vitally important that he not be an OBVIOUS con man, so Van Dyke's outwardly ingratiating and charming personality arguably made him the perfect choice for Harold Hill. I certainly thought he sounded like perfect casting before I saw him in the show, but like so many others, I found him tremendously disappointing in the role, and maybe that was due to personal issues he was having at the time.
I think Hugh Jackman is also perfect casting, for the same reasons.