It's an enjoyable read, but the big takeaway is just that people have felt this way for at least as long as people have been able to write about how they feel. I think certainly there's a waxing and waning of despair on a societal level, and we may be in the waxing phase at the moment, but despite its relative fluctuations the feeling is eternal. A deep sense of unhappiness is what drives us to strive for a better life. Despair may be eternal but so is hope, and so long as hope is even a little stronger than despair, we're going to come out ok.
I just finished reading a book called The Lost War which was written by a Japanese reporter in 1946. Japan in 1946 was one of the biggest pits of despair history has ever known, and even the Japanese people found reason for hope (the happy part of the book is reading about the kindness and humility of the US occupiers when the Japanese were basically all prepared to be starved and raped). If you can find hope after the sacrifice in vain of a whole generation of young men and the leveling of essentially all of your cities, then you can find hope anywhere. People are strong.