First of all, I have the impression that he's incredibly vain. Maybe that's not entirely his fault, because parts of the left in Europe celebrate him like a rock star. But when he retells the story of how he negotiated with other leaders of the EU about the Greek debt crisis, the framing is always that he was the only wise person in a room full of idiots, and they wouldn't agree to the rational course of action because they were intimidated by his superior intelligence. This is of course just my observation, and I don't have a good source ready, so I'm curious if others have the same impression.
Second, although he downplays it somewhat when asked directly, he is a full-on radical marxist. This includes the view that anytime someone makes any money anywhere whatsoever, that can only mean somebody else is being exploited. I don't know how marxists square their conviction that no trade is ever beneficial to both sides with the reality that nobody is held at gunpoint to make those trades, but here's an example quote from the interview:
> So, when a recession hits, and the central bank decides to stimulate the economy, the central bank lowers the interest rate of the overdraft it grants commercial bankers – who then exploit this to profit from arbitrage (by lending the money on to customers at a higher interest rate).
I find this incredibly disingenuous because as an economist, he knows better. Lending is a service that banks provide that many (arguably perhaps too many) people choose to make use of. And Varoufakis is fully aware of the difference between risk-free and risk-adjusted interest rates. But of course, "banks bad", that's what his audience wants to hear. I think there, he agrees with the crypto people to a much larger extend than he would admit.
TL;DR: I think Varoufakis is overrated, although I somewhat agree with him on crypto.