Travolta is one of those actors (and I use that term loosely), where, whenever I am watching him on screen, I am very aware I am watching John Travlota. I never see whoever his character is supposed to be, I just see John Travolta. If you are always basically yourself on screen, and you are, say, Cary Grant, that is ok, because you are Cary Grant. If you are John Travolta, it is not.