口语化的“这是一个好人”怎么说？

直接赞赏对方就说What a good man you are !
若是赞赏第三个人（转述给听话者）就说What a good man he/she is!
[同二楼(注:女的也可以说成man,这是一个泛指) ]
这样语气更好

it's a good guy .也可以 这种很随意的口气也是英语中（口语）常用的

He/She is a kind/good man(注:女的也可以说成man,这是一个泛指)

He is a good man.

he/she is a good person

That's a good guy

That's a good egg.