What's your opinion about/on this plan?
Some people always have strong opinions.
He didn't express/give an opinion on the matter.
Who, in your opinion, is the best player in the league?
Her opinion of Adam changed after he'd been so helpful at the wedding.
I want to get a second opinion on whether I need knee surgery.
I really enjoy shopping for clothes especial[l]y when I go shopping with my brother, because I sometimes ask him for his opinion. (Preliminary English Test; B1; Arabic)
The advertising campaign is intended to influence public opinion.
There is a wide range of opinion on the issue.
We have a difference of opinion among the committee members.
Opinion is divided as to whether the treatment actually works.
Both performances were excellent, it's simply a matter of opinion as to whose was better.
I would like to add that when it comes to public opinion there is a great variety of different points of view - that is why this article, which asserts that "performers were second-rate'' seems to be unfair. (First Certificate in English; B2; Russian)
He has a low opinion of doctors.
He had a very high opinion of this particular course. (Certificate in Advanced English; C1; Polish)
In my humble opinion, that's the wrong decision.
In my humble opinion, there's no such thing as a uniform celebrity, good, bad or otherwise. (Certificate of Proficiency in English; C2; Russian)