Use 'crestfallen' to express someone's visible disappointment; their emotions are not hidden. Her crestfallen face at the party showed she didn't get the anticipated promotion.
Pro Tip 2/3
Intensity
'Crestfallen' implies a strong feeling of disappointment, not a mild one. He stood crestfallen as the award he expected went to another.
Pro Tip 3/3
Not Just Sad
'Crestfallen' combines sadness with a sense of deflated pride or hope. Once a confident speaker, he was crestfallen after forgetting his lines on stage.