enttäuschend
disappointing
Something that does not meet expectations or hopes and therefore causes a feeling of disappointment.
Das Ergebnis des Spiels war für die Fans sehr enttäuschend.
The result of the game was very disappointing for the fans.

disappointing
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disappointing
Something that does not meet expectations or hopes and therefore causes a feeling of disappointment.
Das Ergebnis des Spiels war für die Fans sehr enttäuschend.
The result of the game was very disappointing for the fans.

The word comes from the verb 'enttäuschen' (to disappoint). This consists of 'ent-' (away) and 'täuschen' (to deceive). Originally, it meant to free someone from a deception or illusion, which often leads to disillusionment.
Ich will dich nicht enttäuschen, aber das wird nicht funktionieren.
I don't want to disappoint you, but that won't work.
'Enttäuschend' (disappointing) can describe not only a noun, but can also be used as an adverb to evaluate a verb or the whole sentence. It then remains unchanged.
Die Mannschaft hat enttäuschend gespielt.
The team played disappointingly.
This adjective is often used to evaluate the result of something. Typical nouns are: 'ein enttäuschendes Ergebnis' (a disappointing result), 'eine enttäuschende Leistung' (a disappointing performance), or 'ein enttäuschendes Spiel' (a disappointing game).
Nach der langen Wanderung war die Aussicht leider enttäuschend.
After the long hike, the view was unfortunately disappointing.
bitter
'bitter' and 'enttäuschend' can both describe a negative experience. You use 'enttäuschend' when something is worse than you had hoped or expected. 'Bitter' is stronger and more emotional: it describes an experience that hurts, seems unfair, or is hard to accept. So a result can be disappointing because it is not good enough. It is bitter if it is especially painful or hard for someone.

Die Leistung des neuen Handys ist enttäuschend, weil der Akku nur wenige Stunden hält.
The performance of the new phone is disappointing because the battery only lasts a few hours.
Die Absage kurz vor der Reise war für die Mitarbeiterin besonders bitter.
The cancellation shortly before the trip was especially bitter for the employee.