Controversial in the very least. I also got the impression that he was quite anti-EU with his whole Greece rhetoric during the discussions about another Greek buyout. Maybe I got him wrong..?
Here is an interview that explains his position a bit better than my paraphrasing: https://amp.theguardian.com/books/2017/mar/07/yanis-varoufak...
He may be good at writing books or giving lectures but he was a complete disaster as minister of finance.