My personal rules of Kokoro-chan's facial expression.

*Bad*

*Good*

No highlight in the eye.

Eyebrows never move.

No blushing on the cheeks, but can sweat.

Mouth shouldn't open more than necessary.

Note: These are just my personal definitions. I have no intentions of forcing them onto others.

At a level where one doubts the existence of her facial muscles.

Because she's full of emotions but doesn't show facial expressions, her body language is overreacting.