I think that the main reason this book garners such mixed reviews these days is because in many ways it has dated quite badly. It's nearly 40 years old, and sometimes it shows. On the positive side, it is still a fascinating ramble through the history of Magic and Spiritualism, and its most famous practitioners (John Dee, Aleister Crowley, Madame Blavatsky, Daniel Douglas Home, Cagliostro etc etc). When he's talking about them the book is very absorbing indeed. Wilson also comes across as being on some kind of mission, to get the reader to develop their minds and reach out beyond the mundane and the narrow. This is all very laudable, particularly in this superficial day and age, and at times it's highly stimulating, at other times it can feel like he's nagging!
What I felt let the book down for me is when goes off on tangents that aren't really very interesting, (when you've heard one case-history of reincarnation, take it from me, you've heard them all) which I suppose is inevitable is a work that is nearly 800 pages long. Wilson can at times be far too self-reverential, and also he isn't always objective enough. He blindly adores Gurdjieff, (who just comes across as something of a bit of a a dreary old fart), has very 1950s views on women and homosexuality (the best of which I can say about these views is that they are "quaint"), and some of the paranormal incidents he narrates are dodgy to say the least. For example, when discussing Spontaneous Combustion, he cites the hoary old tale of Maybelle Andrews bursting into flames when dancing in a Soho nightclub many years ago. This would undoubtedly be a tragic and disturbing story ... if Maybelle had ever existed. She didn't. Some writers and journalists took the case of a young woman called Phyllis who died of severe burns after a discarded cigarette set her party frock alight, and turned it into Maybelle spontaneously combusting.
All trashing aside though, this is still a book I fully recommend for anyone who is interested in the history of the paranormal, and Mr Wilson, (a very well-read man), leads us through it in a nicely painless way.