I think one of the big problems is how drastically different a character can be perceived by recasting the voice actor. Howl (of Moving Castle fame), for example, seems to almost have an entirely different personality when given Christian Bale's gruff voice compared to the original. I think there's probably some intentional westernization going on with the voice-casting, and it's not that they're going to make the movie bad by altering your perception of certain characters, but I fundamentally believe that it's always best to experience an artists work as directly as possible, and it's especially off putting when they play fast and loose with such an important aspect.