Appeal
'Appeal' is that indefinable x-factor that makes the animation attractive, not in any specific sense. You should look to find ways of making character design and action memorable in some way. That doesn't mean any one type of style, exaggerated or pretty, but with animation there are infinite ways of making a lasting impression on an audience.
Aardman's classic character, Morph, is a good example of the value of joy and simplicity. You don't need to over-complicate your characters and they may be just as effective with a simple design. Plasticine defines his nature, how he moves. Keep in mind the medium you're working with, can you use it to its full potential? See if you can find the particular qualities of 2D animation, 3D computer graphics or stop-motion to make a more appealing film.
This character sheet for Aladdin demonstrates the value of shape when designing characters. We can read a lot about personality from the body, and here it is reduced to an essence in shape. Animation is a visual medium and the viewer can read much into a character before they even open their mouth, if they do at all. Consider exaggerating your initial designs into a bolder, more memorable form.
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Simpsons creator, Matt Groening, has cited classic cartoon designs in his imagining of the Simpsons family. He observed that the great characters like Bugs Bunny and Mickey Mouse were all instantly recognisable in silhouette, and so every Simpson's hair outline is unmistakable to each character.
'Appeal' is like charisma. Be open to playing around with alternative designs, you might not know why one thing works better than another.