He is a VERY CREATIVE person, writes, paints, sculpts, makes music, does computer games, etc. So his approach is more that of an artist than a psychologist or philosopher. He says what he has to say in a pretty poetic way, not so much an academic way, much of the time. Which may or may not work for you.
He's a bit of a trickster and a guy's guy. (Meh for me, but great for others!

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"The American Book of the Dead" is a bit of a classic. Reading it won't hurt you any...Or listening to it, even more evocative!
Some of his work is very dense: "The Human Biological Machine as a Transformational Apparatus" ~Ooof! I read it and I don't recommend it unless you are a devoted student...
Here's a quote about him from wikipedia: "Gold has for many years acted as an independent spiritual teacher whose work and style bear a strong affinity with the teachings of G.I. Gurdjieff and the Fourth Way school of thought. Gold's particular style, as evinced in his published writings such as The American Book of the Dead also demonstrate a strong influence of Tibetan tantric teachings such as the concept of bardo or "in-between" states. Like Gurdjieff, the fundamental emphasis of Gold's teaching is on the concept of spiritual "Work" in daily life and a constant effort to increase and maintain heightened awareness in all activities. The state of an individual "in the Work" is thus contrasted to what is taken to be the state of the "ordinary" unawakened individual, who is presumed to go through life in a condition of quasi-automatism or mere social conditioning ("asleep," in the metaphorical terminology of this tradition..."
Pretty accurate summing up, so far as it goes, in my experience!
Any of these books would be a little more accessible if you're just curious and want to dip into his work a bit. Get them from the library, or buy them cheap used. Gold's work is not to everybody's taste, but interesting:
Alchemical Sex.
Angels Healing Journey.
Autobiography of a Sufi.
Bardo Stations: A Guidebook for the Afterlife.
The Book of Sacraments.
Brother Godfrey's Journal.
The Hidden Work.
The Invocation of Presence.
The Joy of Sacrifice.
The Lazy Man's Guide to Death and Dying.
The Original Handbook for the Recently Deceased Workbook, Manual, Practicum. (with Dr. Claude Needham)
Secret Talks on Voluntary Evolution.
The Seven Bodies of Man.
Secret Talks With Mr. G.
Shakti: The Gestalt of Zap.
Songs My Dead Mother Sang Me. (with Parker Dickson, et al.)
Tanks for the Memories. (with Dr. John C. Lilly)
(That last one is about floating in a sensory deprivation tank as a means of exploring one's being and consciousness.) Great fun!!!
I have De Ropp's "The Master Game" in my library, but would like to also read his autobiography, "The Warrior's Way." Oh, Santa!