Three dimensional is movement in space. The fourth dimension is movement in time. A live performer has charisma. An animated character has appeal. Appealing animation does not mean just being cute and cuddly.
All characters have to have appeal whether they are heroic, villainous, comic or cute.
Early cartoons were basically a series of gags strung together on a main theme. Over the years, the artists have learned that to produce a feature there was a need for story continuity, character development and a higher quality of artwork throughout the entire production. Like all forms of story telling, the feature has to appeal to the mind as well as to the eye.