Some bad voice over work, eh.
I don't mind the voice being off sync with the mouths. I've seen enough anime as to not let it bother me. But the choices of some of the voices are bad. Such as Jimmy Fallon's character. His voice doesn't fit it at all. Even minor characters, like the old dusty Minimoy that Arthur meets when he's first shrunk, didn't have the "right" voices. And finally, Madonna's voice over work is just horrible. On another note, she never looked better.
I still enjoyed the movie. The animation was top-notch. I loved all the lighting & particle effects. Made the world of the Minimoys seem realistic.
----------------------
Those who think they are always right are annoying to those of us who are.