I can only agree with your rave review of the book after having read it twice and having a few sleepless nights because I was unable to put it down.
I wonder if you've read another book by Rhodes called Masters of Death -The SS-Einsatzgruppen and the Invention of the Holocaust? It examines the whole story of the formation of the different Einsatzgruppen their mass killings behind the Russian front which were so enormous that even today the number of their victims can only be guessed at. I highly recommend it after having recently read it in pdf format.
I am sorry to say I have not read either of the books. Perhaps the author of our review has read the one about the Einsatzgrupen.