Shouldn't really be called "...Interpretation of Sadism, Masochism..." because the touching bases of those two topics are indeed just that, touching base; which he does twice for Sadism, in the beginning and end, and once for Masochism (in the beginning, but he seems rather uninterested in mans' inclination toward punishment/pain). It would rather, more appropriately, be called "An Interpretation on the History of Human Violence through Anthropological Hypothesis Involving the Origins of Lycanthropic Folklore."
I found his thoughts on the history of lycanthropy interesting, as having read up numerous writings on the legends from all over the world of strange mystical beasts, and found also interesting his idea of where the Genesis story of the Garden works in to a non-biblical belief in human development. I, however, don't believe mass-psychology can produce something inherently in a man or woman, so disagreed with much of it, though. If this isn't an issue for you, then you'll find it something to mull over.
All in all, he had a few little gems of things I wish he had actually thought to talk about, but I think he lost his way in the Jungian archetypes of dreams (which seemed to me to prove nothing but that one may interpret one mans dreams for ones own needs), and the anthropological explanation as to why some tribes of people seek violence against others, and some don't. No real evidence or even theory as to Sadism or Masochism, or how we might, indeed, find a way to prevent war, or stave off our blood lust, was introduced; but I think we should give him points for discussing a subject that was quite out there to discuss during the time period it was presented.
An amusing anecdote (I found) was the poor homosexual man who was encouraged by his doctor to pursue the "normal" life of seeing a girl that fancied him, and his dream of hurting her... Sigh... No, it doesn't mean we are archetypes of werewolves, Mr. Eisler, and no, I don't think that he means to harm her. I think he's just a poor frustrated guy. Give him a break (after all, he's probably dead now, too).