What to look for in examples:

How do you define the emotion? Be precise as possible.

What features are used to convey the emotion?

Is it the static position of the features, the quality of movement of the features or a combination of the two? What is it about each which conveys the emotion? Pay particular interest to how the features change over time.

How is staging (e.g. position of camera and lights, relative position of characters) used to heighten the expressiveness of the movement?

Is sound/speech used? If so, how? If you turn off the sound, can you still distinguish the emotion?

How un-ambiguous is the emotional state of the character? Is more than one emotion being conveyed at a given time?

Is the reading of the expression context-free, or do you have to know what has previously happened in order to understand the expression?

Is there anything particularly unique about how the character expresses the emotion?

Could you implement it in an interactive character? What would be easy, what would be hard?