I'm glad you understood.
I was truly glad.
You understood well
I shouldn't have done that kind of thing.
I'm so glad that you succeeded.
良いことをした。
You have done very well. It does you credit.
I thought that was cool.
よし, よくやった.
うまくいった。
That worked.
It was lucky.
He has done it better than I expected―beyond expectation―beyond my expectations―surprisingly well.
よくできてたよ。
You did great.