I have been looking for this book for some time. It was not easy to track down - an Amazon Marketplace order failed to find it in over a year, eventually I found a copy on eBay, and then even that took almost two months to reach me from the California dealer (plus I had to pay €10 customs on it).
It was worth the wait. This is easily as good as the other two and a half books I've read about Zelazny (by Theodore Krulik, Jane Lindskold, and a much shorter effort also by Yoke) put together. Unfortunately it was written in 1977, less than halfway through Zelazny's writing career, which was cut short so prematurely ten years ago next month. Fortunately, it still covers what are generally considered to be Zelazny's best works. There is a chapter each on "A Rose for Ecclesiastes", This Immortal, "The Doors of His Face, the Lamps of His Mouth", The Dream Master, Lord of Light, "Home is the Hangman" (and the other two stories in that series), and the first five Amber books. Each of these is about ten pages long; I see that Yoke is an associate professor of English at Kent State University, so perhaps that explains why they read a bit like notes for a lecture course.
I found Yoke's exploration of the layers of myth and meaning behind Zelazny's early great work very enlightening. The most densely packed chapter is the one on The Dream Master and the Arthurian mythos. The most interesting, for me, was the one on "The Doors of His Face, the Lamps of His Mouth", exploring its parallels with the Book of Job (which reminds me that I am still working on a piece on Ted Chiang's "Hell is the Absence of God" for my website). It was also interesting to have flagged up front the recurring symbolism of the rose in "A Rose for Ecclesiastes" and the Amber books, and other uses of dance, water, and rings. And I found his explanation of Zelazny's themes of form vs chaos, maturation and heroism, very convincing.
Having said that this is the best book I have found about Zelazny, there is surely scope for a better one. The prose is sometimes repetitive, and occasionally mises obvious points - for instance, while I am persuaded that it is important that Render, the name of the hero of The Dream Master, means "to represent or depict", surely it's also important that the word can additionally mean "one who tears apart"? Several chapters rely too heavily on a single authoritative theoretical source (Peters' Rilke, for instance for "A Rose for Ecclesiastes"). And I simply can't agree that Flora and Fiona are difficult to distinguish in the Amber books!