Like all history books the book inevitably come across a lot of data and details, which are probably quite meaningless to laymen. Seriously, 4 millions deaths or 3.5 millions deaths doesn't make any difference to me. But apart from these details, the book is good at juxtaposing the social catastrophe resulted from both Nazi and Soviet Terror, which makes the readers completely appreciate what beyond imagination means. At the same time it gives a vivid account of their difference on ideology, which is very interesting. The book also sketches the characters of Lenin, Stalin and Hitler, which, I think, is essential to understand that part of history.
Now I still linger on the question, how come the capacity of being evil can be as infinite as that? Too bad this book, after all, it's about history only, can't answer the question.