DISAPPOINTED がっかりした

To be disappointed (adjective) is to be unhappy because something or someone is not what you hoped for or expected.

To disappoint (verb) or to BE disappointing (adjective) is to cause someone to be unhappy in this way.
disappointed （形容詞）は、ものや人が希望や期待通りではないために不満だ、という意味です。

動詞の disappoint や、形容詞を使ったBE disappointing の表現は、誰かを不満にさせる、がっかりさせる、という意味です。

DISAPPOINTED

I'd heard such good things about the hotel, but I was disappointed with the small room and bad service.
I'm very disappointed in you. That's the second time you've broken a promise.
(teacher to student)
I was disappointed to learn that you won't be applying to any colleges.
(sister to brother)
Mom was very disappointed that you didn't send her a card on her birthday.
COACH: You'll be the starting pitcher for tomorrow's game.
PLAYER: Thanks, coach! I won't disappoint you.
I'm sorry to disappoint you, but I've already rented the room to someone else.
The weather has been rather disappointing so far. We haven't seen the sun since our plane landed.
She had a disappointing finish in the last race, coming in 5th among 6 runners.

英会話レッスン If you come back tomorrow expecting another fine edition of Berlitz WordMaster, well, you won't be disappointed!