Having made the connection between Siva and Dionysus from other sources, I looked forward with some anticipation to a book that treated both together. I have come a way a little disappointed. While the book is well documented and very factual it lacks poetry. I could not get a feeling for either of the Gods from this book as I have been able from others (Like 'Dionysus: Myth and Cult' by Walter Otto.) However it was reassuring to to have my intuitions about the link between the two Gods substantiated.
The bulk of the material is about Siva, (which is understandable given the background of the author and the relative amounts of material available on each of the subjects) though this leads to a somewhat fragmentary portrait of Dionysus.
In places it has the tone of a polemic for a return to 'natural' or 'ecstatic' religion as a basis for saving the planet. It treats the 'good' features of such an approach at length but fails to adequately address the fact that 'Siva/Dionysus' is at heart a 'mad' and ambivalent God (CF. W Otto above). I am not sure I can stomach a return to ritual or cult prostitution or to human sacrifice. Feminists may be interested in his description of the 'natural' role of women.
At first he appears to be anti-christian though this turns out to be more anti Roman-Catholic and Institutional Church. He believes that Christianity in its original, unadulterated form was very close to 'natural' spirituality and points to the many parallels between Dionysus and Christ.
I would suggest that readers get a good background in both subjects before reading this book.