The accent is my main issue with Americans in that kind of setting. Costner played a good part but the accent kinda ruined it. Also, I've never seen Willow but I've always heard that it's pretty good.
Like I said about doing a movie, Miyamoto should be actively involved in the writing since he created the franchise. That or at least have him as a consultant like JK Rowling was on the Harry Potter movies.
Also, British actors would fit the theme better. Never thought American actors really...