Honestly - I didn't understand it, or at the very least, I suspect that I may have grossly misinterpreted its purpose.
The first confusion is that for me, there was an apparent shortage in metaphysical grounds that persisted throughout the text, primarily concerning the question - of what substance am I to consider Dionysus, or his energy? Surely Johnson was not positing that I interpret him as a literal god, but if so, then what specifically does he intend? If he is a mere 'force of nature' or 'condition of the psyche,' then why choose to deliberately incorporate seemingly haphazard elements of Greek mythology, Jewish tradition, Christian theology, modern consumerism, Jungian psychology, until the resultant creation is nothing more than an ambiguous tapestry of no credible telos? And furthermore, if Dionysus is an energy or a persistent element of the cosmos, then why name him Dionysus, invoking an arbitrarily archaic creation of the Greeks?
The book is riddled with other ambiguities - Johnson frequently invokes pithy aphorisms in the vein of "do not deny yourself the Dionysian experience!" but without fully providing the definitional groundwork of what constitutes such an experience. If I am to assume that I have in fact, completely understood the book's contents, then I am saddened to say that all of its arguments and constructive material can be refuted without great effort.
The book concludes with hurried and insufficient recommendations on the conducting of rituals in the spirit of Dionysus, but as far as texts on rituals go, this one seems to be lacking in an expansive quantity of elaboration before an effective one may be carried out. I admit to being at most, rudimentary in my studies on ritualistic practices, but even from my limited vantage point I can note that there are very key elements absent - symbolic objects, incantations, or any material objects that are necessary in for a novice to fruitfully connect the spiritual with the physical. In short, I believe that the summary on ritual from this book can be fairly understood as "anything is ritual" - which is an observation that is impossible to fully deny, but is also fairly generic and unambitious.
As a footnote, I will confess that I had interpreted the word "psychology" in the title in a vein that is more modern and quite removed from its Freudian, psychoanalytic sense. Perhaps I should have adjusted my expectations when the inner cover specified that the work was composed by a Jungian scholar, but with that being said, I still did anticipate the book to be far more focused on the degree to which euphoria influences our lives, its recommended dosage, its comparative to the eudaimonic experience, historical figures who have emulated the ecstatic lifestyle, etc. What I got instead seemed to be the abstract musings of a slightly tipsy preacher who is more intent on creating grandiose depictions of his own delights than anything that would truly intellectually stimulate a reader.
That being said - this book confused far more than disappointed. I have written this review under the assumption that I have not misinterpreted any of its pages, including its overarching end goal. Notwithstanding, it is entirely possible that my judgements be uncharitable and that the true reason for which this piece was not enjoyable was due to my own deficiencies as a reader.