Clear visual communication via shape language, posture, and dynamism between elements of the character. Like Sora in Kingdom hearts, his clown shoes and balloon pants give him a unique look that you could spot in any silhouette.
All of the best character design comes from the 2D animation and the games industry. None of the modern Pixar stuff can keep up with the early disney designs.
Dragonball characters, Nintendo characters, early video game mascots, early Disney characters, all of these have immaculate shape and color design beyond skill or detail or uniqueness.
Even Dark Souls or Bloodbourne succeeds at this while being detailed and dark, they have great angular shapes in their designs and a somber, dreary posture.
A good character design packs as much information into the subtlest things as possible while keeping things simple and clean.
