I completed volume 4 of this series probably ten years ago, so it's been a while since I was wading into Huxley's essays. I have read a great deal of Huxley's output, both fiction and non-fiction, over the years, so I knew fairly well what I was getting into, but I still found this book to be punishing and a difficult undertaking.
The bulk of the material in this volume is from two of Huxley's collections of essays: Adonis and the Alphabet and Themes and Variations. Also included is the Doors of Perception, the long essay for which the band the Doors were to take their name.
Huxley is at this juncture in his career more or less fully immersed in the mystical and drug-induced transcendence seeking leg of his journey. The essays range over a variety of topics, but concern over the earth's population is a big theme, as well as seeking ways to rectify man's experience with reality as it exists with his perception of reality as as a series of symbols, and the concluding section deals with thoughts about various artists, mostly painters and musical composers.
It's clear that Huxley is enormously intelligent and the breadth of his reading is expansive. On the other hand, many of the essays seem to get sidetracked or just be generally meandering, especially when the reader is coming to them devoid of context 70+ years after their publication. I don't think you can really gin up much an argument that these essays are of interest to a general audience, though it's laudable that someone has taken the initiative to collect them all. No doubt it was very hard to find many of them prior to their re-publication in this format.