Adding to what others have said about the book, what makes it exceptional is the author’s clever use of a ‘hot chronology’, where she’s documenting events minute by minute (and there are fewer minutes than you’d expect before total global annihilation, which is the whole point).
There’s a lot of content, it is very skilfully researched, and it merits at least two readings. Not all aspects of the scenario are as viable as each other (I found the US/Russian total communications failure the most unlikely, given it was being actively blocked at all levels in a way that was most emphatically not in Russia’s own interests, so someone there would have agitated for communication) but it’s a book, not a report.
What I found interesting was the psychological vacillation I experienced while reading it, flipping between being determined I wouldn’t retaliate, to wanting to retaliate to protect other nations and regions, as more information unfolds. It gives a good idea of the horrendous competing pressures people are likely to feel when making such decisions.
I’d put this book in the same category as Neville Shute’s ‘On The Beach’ for alarming poignancy, and agree it should be required reading for young people aged 16+. I would add that everyone in the military and politics should read it too, so they try harder to find common cause.