I have watched plenty of his talks and interview. His book is probably too depressive.
That's... likely indeed, but someone who still comes out as a fervent pro-european after all of that really can't be doubted anymore
It's a long story.
Basically, for political reasons, the Troika which was mostly led by Eurogroup which itself was motsly led By Schauble was just firm on using Greece as an example to keep others southern countries in line, no matter what reasonable plan Greece would put forward or any argument they would try to make, anything would be followed with nonsense answers like "BLABLABLA WE DIDN'T HEAR YOU", "LET'S JUST STICK TO THE CURRENT PLAN ("that we know isn't working")
Both IMF (through its president Christine Lagarde) and ECB (through Benoit Coeure its vice president) were rather agreeing with the various options put forward by Varoufakis but, facing incredible pressure, were forced to follow what was set by Eurogroup as they weren't able to take an opposing political stance (IMF has communicated multiple times afterwards to say how austerity in crisis time was just a big mistake in the end)... but at the same time Schauble was a big advocate of Grexit (still to make an example out of the country) but wasn't able to go all the way because that wasn't Merkel's intent (coincidentally, the Ukrainian crisis was happening at the same time)
Varoufakis had this terrible revealing thought "how do you want us to pay debts our creditors don't even want to recover", Schauble didn't care anymore about the debts, Jeroen Dijsselbloem was just a dumb bully that knew nothing about economy, ECB kept saying they couldn't take a political stance despite doing so multiple times beforehand, IMF was powerless as well, France was made of your typical nice people in private that either bowed to Deustchland or were powerless (Sapin, as he said knew nothing about economy as well, Varoufakis did have some nice words about Macron but he couldn't do anything) even in Greece there were litterally greek Troika's spies openly going around sabotaging any attempt of coming up with a new reasonable plan that would stop the humanitarian disaster that was still going on.
The European Commission (Moscovici) were just some useless buffoon that agreed with plans they discussed with Varoufakis in private but bowed afterwards and were agreeing to the opposite they said in public, Varoufakis described that as the "death of a certain idea of Europe" (where the comission is basically useless)
The book is overall an endless fall where you see all the terrible politics and bureaucracy that are wrong in the way Europe currently works, how they did everything possible to undermine anything attempted by Greece, how they tried to divide the Syriza government and how Europe, in the end, sacrificed a whole country, millions of people lives in some terrible situation that satisified no one in the end.
The above summary only focused on the Europe inner workings, there were some fascinating things about Greece (including lots of positive) and hundreds of tidbits that make it an incredible read.
Mind it's only the words of one guy in his book, but considering his past works and what we kinda already know about every people he mentionned there's... nothing so surprising, it's just appaling to see it happening before your very eyes page after page while reading.