1. What is his opinion like?

Question

2. What do you think his opinion is like?
- I don't agree with him about his opinion.
- I don't agree with him on/about the statement that his old master was careless.
- His opinion is wanterful.
(Are they all acceptable?)

3. His acting is great.
4. That makes two of us.
5. You can say that again.
6. I think so, too.
7. I agree with you.
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The last four sentences are the same in meaning, right?
Why is the expression in #4 used? Could you explain the meaning of #4? Thank you.

Answer 1

Note my corrections:
1. What is his opinion?
2. What do you think his opinion is?
- I don't agree with him about his opinion.
- I don't agree that his old master was careless.
- His opinion is wanterful. <~~Do you mean "wonderful"?

Sentences 3-7 are correct.
Sentences 4-7 mean about the same thing.
Sentence 4 is a colloquial way to say sentence 7. (The two people -- the speaker and the person being spoken to -- agree.)