Hair and Outline
. If an audience or populace can recognize a character just by their outline (their shadow), then you have an identifiable character. Case and point: Tetsuwan Atom. Show an outline of his head or body to anyone in Japan and I expect the vast majority would know instantly who the character was, even if they never saw the show (the same is true for Mickey, Homer and Bart, Totoro, and a few other animated characters).
Everything else is subjective (CA wrote more or less anything I could write here).
edit: I think there was a thread here a few years back all about character outlines/shadows...