Emoción vs. excitación vs. entusiasmo

The Spanish words 'emoción', 'excitación', and 'entusiasmo' all relate to the concept of emotional arousal, but they differ in nuances and contexts.

Emoción

'Emoción' refers to a strong feeling deriving from one's circumstances, mood, or relationships with others. It is a more general term for any strong emotional experience.
Sentí una gran emoción al ver a mi familia después de tanto tiempo.
(I felt great excitement seeing my family after so long.)
La película despertó muchas emociones en los espectadores.
(The movie stirred many emotions in the viewers.)

Excitación

'Excitación' usually denotes a high state of physiological arousal or intense excitement. It often has a physical or even an erotic connotation depending on the context.
La noticia causó una gran excitación entre los fans.
(The news caused great excitement among the fans.)
El atleta sintió una gran excitación antes de la competencia.
(The athlete felt great excitement before the competition.)

Entusiasmo

'Entusiasmo' refers to intense and eager enjoyment, interest, or approval towards something. It indicates a more positive and motivational kind of excitement.
Su entusiasmo por el proyecto contagió a todo el equipo.
(Her enthusiasm for the project spread to the whole team.)
El niño mostraba un gran entusiasmo por aprender a tocar la guitarra.
(The child showed great enthusiasm for learning to play the guitar.)

Summary

While 'emoción' is a general term for emotional experiences, 'excitación' emphasizes physiological arousal and can have physical connotations, whereas 'entusiasmo' conveys a positive, eager interest or enjoyment. Choosing the correct term depends on the specific context and nuance you wish to convey.