Ellison lays out the basics of Celtic Paganism in a scholarly yet accessible way. He supports each of his assertions about Druidic beliefs and practices with citations from ancient sources and from archeology, and lays it all out in an outline that allows students to get started immediately with a Druidic spirituality. Far from being duotheistic, the book gives advice for constructing your Druidic pantheon of worship based on the realities of the local land, and the spirits proper to each individual worshipper. From there, he presents a full system of Druidic ritual, as used in Ar nDraiocht Fein - about as far from a Wiccan form as one could get. It involves offering to the Gods & Spirits, divining their blessing, and then receiving that blessing. Ellison gives solitary rituals for each of the Celtic holy days (and for the solstices and equinoxes), as well as ideas for Druidic funeral and wedding rites. There is a section on spells and practical magic as well, and the book ends with a listing of every Druidic group and order of any size at all. This is a valuable resource - one of the very first books on Druidry drawn from a non-wiccan, scholarly perspective, adapted to practical use.
A useful resource for absolute beginners, but for anyone who has any experience in the pagan spaces this book is mostly just rehashing a lot of information and providing questionable facts. The heavy reliance and Kondratiev is disappointing considering his book is based around the idea of building Celtic rituals that honor cultures and language rather than deities or kindreds. His information is generally recognized as useful, having him as the sole source for so much "pagan" folklore is worrying. There are definitely better books for pagan practice and for anyone who has basic experience in writing solitary rituals the utility of this book sinks rapidly.
I'll be honest. This wasn't my favorite book on druidry. It's not a bad book by any stretch and for the individual who wishes to learn about druidry from a more American perspective and gain a good understanding of the history and basics of ritual, it is helpful. But I did find some of the ritual templates a bit repetative and the history a bit dry and requiring more research. So- not a bad book, just not my favorite.