This book is simply excellent, it contains over 10,000 entries on ancient gods and goddesses as well as other mythological figures like Satan, King Arthur and archangels. The book has entries on almost every culture going, Persian, Greek, Indian, Roman, Germanic, Anglo-Saxon, Celtic, Aboriginal, Japanese, Slavic, Babylonian, Sumerian, Native American and many more.
The encyclopaedic entries themselves are not greatly detailed but they do provide enough information on various the gods to initiate further study -- some entries are more detailed than others depending on their "importance" for example, Zeus has a larger entry than the Titan god Prometheus. There are one or two more obscure gods and goddesses that I've noticed are missing (Herodias for example) but this isn't a big issue; as 99.9% of the gods and goddesses I have looked up have been easily found in this book (I believe there were only two that were not in the book).
One helpful feature of the book is that it also indicates other entries of interest and notes different names by which the god or goddess was known by. For example, with Hecate (Greek Underworld goddess) the book indicates the other goddesses related to her, which are 'Artemis', 'Diana' and 'Demeter' etc and some of her epithets: 'Brimo Crantaeis, Endonia, and Proserpina.'
A must for people interested in mythology and Pagans.