Harris' book is the published form of a personal grimoire, compiled over a long time. As such, it is dense in information and has a fresh and immediate style - it's as enjoyable to dip into as to read in longer sittings.
There is an even mix of practical methods, history and lore, and the structure is fairly loose and easy going. The author never presents himself as authoritative, but rather more as a fellow magician, a friend who is sharing the things he has learned and/or discovered. There are many spells and rituals in the book, which the author has in the main successfully undertaken himself.
Harris is clearly widely read and has personal experience of a variety of magick traditions, but above all certainly understands what it is all _really_ about.
To be honest, Witcha is perhaps the best book I have ever read on the subject of witchcraft (and certainly the one I have enjoyed the most), and perhaps the only one I have read which treats 'black magic', or the left hand path, equitably, sensibly and from a more enlightened perspective.
If you're a newcomer to witchcraft, or perhaps a Christian or Muslim keen to learn about the 'opposition', you'll find the book chock-full of things you want to know, presented in a straightforward and accessible manner.
If you're and old hand, you'll find much to agree with, and will enjoy Harris' style; free of the pomp and wordiness often found in esoteric texts.