多令人失望啊!

How disappointing!

真令人失望。

It's disappointing.

我很失望。

I'm rather disappointed.

你让我失望。

You let me down.

他没有我想象的那么好。

It wasn't as good as I expected.

真可惜。

What a shame!

很可惜。

That's a real pity.

太糟糕了。

That's too bad.

那只是白费力气。

That was a waste of effort.

都是我不好。

It's all my fault.

我搞杂了。

I screwed up.

白费我那么多的努力。

All that for nothing.