When we talk abut round and flat characters in fiction, it's merely a distinction between developed personalities and undeveloped ones. "Four-dimension" just takes the analogy too far. It's meaningless. It'd be like me saying that the Avengers are infinity times better than the Justice League. It'd be like saying that the Yankees are such a solid team that they have a fifth baseman. Now I've stopped making a rational comparison, and I've descended into fannish hyperbole. For some reason, whenever Harry Potter is involved, this sort of thing is not only permitted, but expected, and it's one of the myriad of reasons I hate his guts. "Twenty thumbs up! Better than heroin! Fun for the entire family, and the descendants of their families unto the fourth generation!"