This is the only book by Richard Gardner I have read. I think it provides a great look into the mind of an esoteric scholar and poet who's exploring the tarot in the mid 1960s to 1970s. However, the language and sensibilities of the author are very specific to that period. There's quite a lot of focus dedicated to sex and sexuality. His beliefs regarding solar/lunar, male/female, fire/water polarities are very dated. I found myself enjoying paragraphs but not entire pages throughout the 157 pages.
For someone who is interested in following the evolution of esoteric tarot lore and philosophy, it most definitely fills a niche. It is not a good book for learning tarot though and there are a number of books published in the last 20 years that cite this as a reference but are a lot more helpful to studying tarot as a psychological tool.
The Tarot is akin to a Mandala and it is possible to apply its archetypal images to the process of self integration. Gardner's exposition is a lot simpler than Jung's but the intent is the same.