There are few books that I have read that have resulted in a similar combination of intense dislike and intense liking as much as this one. To begin with the difficult: JC Powys is not much of a "rigorous" philosopher, and some of the paragraphs in here are rambling and frequently just painful to read. But this is not philosophy like "Rousseau" (to whom the book is dedicated), but it is more of a "philosophy of life" - the creation of a proper mental attitude towards life, rather than an attempt to discover "truth", which is the usual intention of philosophy.
Powys' "philosophy of life," very simply put, is a focus on happiness, obtained through contemplation. As he puts it: "The secret of life is not "Beauty" or "Truth" or "Goodness". . . . It is a certain kind of self-conscious enjoyment that has behind it the full energy and strain of the will." He spends the over-300 pages of this book essentially expounding upon this approach, frequently with passages of amazing depth and insight. This complex philosophy encompasses pretty much everything in life, from our attitudes towards the poor, towards God (what he calls the First Cause), and towards our everyday life. Powys gives Chance a very significant role, and he is particularly strong in his invectives against cruelty. In fact cruelty and meanness towards others are his only "sin".
Happiness is obtained through "sensuality" (an unfortunate word - Powys does not intend it with sexual overtones), primarily it seems, through absorbing nature and life, and thereby obtaining beautiful memories that can be reflected on. While love is important to this process, Powys' vision here is largely a solitary one and not dependent on others. But I would not call Powys entirely selfish, the alleviation of the suffering of others ranks very highly in his view of the role of the individual towards the rest of humanity.
Something must be said about the relation of "Sensuality" to JC Powys' other works. Powys' first great masterpiece of fiction, "Wolf Solent", was made much more comprehensible by reading "Sensuality", in fact, "Wolf Solent" can be read as a sort of advertisement for Powys' philosophy; to paraphrase from elsewhere, it provides "insight into the intellectual structure that forms the metastructure [of the novel]". The two books are very closely connected (even some of the more obscure items such as the reference to "cuckoo-spit"). As a result, reading "Sensuality" makes the main character of "Wolf Solent" far more understandable. On a personal level, I realized while reading "Sensuality" that my intense identification with the character of Wolf Solent was also in part a strong subconscious identification with the philosophy expressed in "Sensuality," which led to my reading of this book being in part a self-revelation.
So I think this work is essential reading for people who enjoy JC Powys' work; unlike perhaps his other non-fiction, it contains the "key" to many of his ideas, including some of the startling ones like the "First Cause" (with which he begins "Glastonbury Romance"), and his concept of the ichthyosaurus-ego (another unfortunate term) is also important. I also view it, as a stand-alone book, as an incredible interesting and worthwhile "philosophy of life", not necessarily as one you might agree with, but one that will cause you to think a lot about how you live.
Note that, as I said up front, much of this work is incomprehensible, but who understands all of "Zarathustra" or many of the other great works of philosophy? This book is in its own very original way, at a "high" level which I think deserves more attention than just being the wild ramblings of a highly sensitive novelist. So I really recommend it to the life-searchers, especially to philosophers, Powys-fans, nature-lovers, but I think he's really writing it for the "lost" who maybe cannot accept or don't want to accept what the world has given them. It is very easy to call "Sensuality" "self-indulgent nonsense", but I don't think, in the end, especially viewed in connection with his novels, that this is the case: rather it is the expression of a distinct and highly unusual philosophy of life with considerable intrinsic merit. While difficult to stomach at first, by the end of "Sensuality" I was convinced that this was a work of great, original, creative genius.