When you're sad because something wasn't as good as you hoped or expected, you can say that you were "disappointed":
I was disappointed because I had hoped we'd get a chance to meet him.
We say we are “disappointed with” something (not someone):
I was disappointed with the new version.
And you can say that you're "disappointed in" a person:
Remember that you use "___ed" to talk about how you feel:
I was kind of disappointed.
And you use "___ing" to give your opinion of something:
It (the movie) was kind of disappointing.
Other words that work in this way are: