I found the Beltane book to be a good general overview of May Day customs and beliefs. It nicely blends elements drawn from various European regions to provide a fuller understanding of how May Day has evolved over the centuries. This book is easy reading and nicely matches the style and purpose of Llewellyn's series on the eight Sabbats. While Grimassi's books in general contain much more depth than this particular title does, it is nice to see his adaptability to a lighter project and this speaks well of his flexibility as a writer.
Because the Celts did not read or write, they have left us little to truly understand about their beliefs and practices. Much of what is known about Celtic religion is drawn from ancient Greek and Roman references, along with texts written much later by Christian monks recording Celtic tales and ballads beginning around the 7th century AD. When one considers that very little is actually known about Celtic beliefs and practices (the majority of writings are speculation) it is amazing that anyone could come up with enough information on Beltane to create an entire book. This fact is a testimony to Grimassi's excellent research abilities, which is the hallmark of his books in general.
The Beltane book is clearly intended for a general audience, but with a strong leaning towards a pagan readership. Even the most casual reader of normal intelligence would not consider this book to be specifically a Wiccan book, and the author never suggests that it was meant to be. Instead, it is clear that Grimassi intended this book to be a nice overview of May Day celebrations and their origins throughout Europe. While some people may feel that the title is misleading since it suggests an exclusive Celtic focus, most people realize that the Publisher has the final say in a book's title (NOT the author) and that the Celtic festival names have become "public domain" and are commonly used by many non-Celtic Traditions today.
To sum up this Beltane book, it is filled with interesting lore about various spirits and characters associated with May along with fairy lore, flower lore, May Day customs, rituals, spells, and recipes and crafts for creating your own May Day celebration. A very nice book and well worth adding to your lilbrary.