I always felt I was a disappointment to my father.

我总觉得我使父亲失望了。

《牛津词典》

It's a disappointment.

太令人失望了。

youdao

The programme has been a disappointment.

这项计划的结果令人大失所望。

youdao

In Europe,politicians and environmentalists expressed deep disappointment that world leaders failed to reach a stronger agreement.

VOA: special.2009.12.26

Disappointment number two, once there is a legitimate government based on consent, the only limits for Locke are limits on arbitrary takings of life or of liberty or of property.

失望的第二点，一旦经过同意建立合法政府后，对洛克来说它唯一的限制,就是不能肆意夺取生命或自由或财产。

耶鲁公开课 - 公正课程节选

This is also an expression used to show a feeling like surprise or disappointment.

VOA: special.2010.02.07

It had been on the cards so it was more of a disappointment than a shock.

BBC: SPORT | Football | Premiership | Jason Roberts column

Eighteen months since its acquisition, most would say that iAd has been a disappointment for Apple.

FORBES: What Is Next For Apple's iAd?

Being seventh after eight games isn't a disappointment even if the recent results have been.

BBC: We will end our losing run - Ward