Varoufakis is a hero to the international working class. His most recent book before this one is also excellent.
He's an interesting guy no doubt, but accounts tell us he was just doing his job. When he went to Germany and tried to force their hands by feigning he might grexit, to his amazement the private response was more or less, how can we help you gtecit? Despite appearances, he did not want grexit and was a ploy to get better terms, but the ecb had already discounted Greece. At least he tried, for sure.
He had a plan (allegedly it was a Plan B) for the exit of the Euro if Brussels (actually Berlin) continue with the craziness. The Greek primer minister decided not to continue with the plan and he resigned as finance minister.
The primer minister could be accused of cowardice, but we have to understand that Greece was threaded with the shut down of its financial system in what, in the opinion of a lot of people, was an illegal movement by the ECB (1). It was a really difficult decision.