John Michael Greer is a prolific writer, organic farmer, peak oil activist and local character. He is also the "archdruid" of the Ancient Order of Druids in America (AODA). And yes, he spouts a large beard!
"The New Encylopedia of the Occult" is Greer's attempt to pen the ultimate reference work on the occult. Not being an occultist myself, I can't vouch for its usefulness, but it does contain many entries I found interesting, and seems to have generally rave reviews here at Amazon. However, I don't think it's suited for the general reader, who might feel plunged into too deep waters, as the author proceeds to tell us everything about the spheres, paths and angels on the Kabbalistic Tree of Life, or enumerates all possible astrological aspects (including a few I'm sure even astrologists haven't heard of). Greer has long practiced ritual magic in the so-called Golden Dawn tradition, which explains the heavy emphasis on related topics. But then, the Hermetic Order of the Golden Dawn was one of the most important Western esoteric societies of the modern era, with figures like Irish poet W. B. Yeats among its members. The Theosophists were even more important, but I'm not sure if they count as strictly esoteric!
Cult-watchers might also find a few titbits here and there, about virtually unknown groups such as Thee Temple ov Psychick Youth, Women's International Terrorist Conspiracy from Hell (abbreviated WITCH), Zos Kia Cultus (whose main cultic act was...ahem...unmentionable due to the moderated character of this forum), Kindred of the Kibbo Kift, Seax-Wica and the Catholic Order of Mopses (a mops is a small, ugly-looking dog). Overall, however, Greer stays away from the undergrowth of the occult world, and there is also very little about black magic, Satanism, sudden suicides among the literati, and other such subjects which other authors love to fill *their* books on the occult with.
But don't worry, our author has actually published another work on sects, cults and secret societies, "The Element Encyclopedia of Secret Societies", reviewed by me elsewhere. That being said, I nevertheless suspect that "The New Encyclopedia of the Occult" is pretty interesting, especially so since it offers a somewhat more civilized perspective on a subject often sensationalized by the media, opponents and occultists themselves...