This is a tough question.
When I think of actors who truly act, I think of Johnny Depp. He changes his behavior and physical behavior to actually create a character.
When I see other actors they seem more predictable. Just as John Wayne was always just John Wayne reading different lines, too many actors say the lines, move around the scenery, and manifest some emotion, but their style and personalities don't actually change.
Think of Arnold Schwarzenegger - he doesn't change his character at all! Emotions - he doesn't have any! Some actors do tend to get themselves fixed towards a certain character and tend to play them over and over again.
