In his forward R. J. Stewart tells us that he has not followed the customary way of separating Welsh, Irish, Scots and Romano-British and Gaulish material, instead he follows his own list as follows:
- The People
- The Mother Goddesses
- The Father Gods
- The Son and Daughter divinities
- The Heroes
- The Kingship and Sovereign Land
- Magical Cosmology.
Also in his forward he tells us that it is not a scholarly work, it is pure and simple Unverified Personal Gnosis (UPG).
R.J. Stewart in his book does have a lot of interesting ideas, which may help people work on their own UPG. He believes that Celtic legends work on three levels:
1. Adventure: Heroic comic and tragic tales presented in early literature.
2. Sanctity of land: The characters are revealed to be pagan gods and goddesses.
3. Stars: Gods of nature are localized versions of cosmic figures.
He also talks about things like Wheel of Being, the four directions and five zones, and multidimensional thinking. It is an easy book to read, not too long and not too short. It talks about many diverse things like how animals, water, rivers, wells figure in the worship of the Celts. But most of all I loved the illustrations in the book.
This work is copyrighted 1990 so right off you know the information is dated, and sometimes it is even confusing. As the author himself tells you this is not a scholarly work, if you are just learning about the gods this is NOT the book to read.
Celtic Scholar's Reviews and Opinions 
I want to read this because I think RJ comes up with some interesting stuff but it’s the kind of thing that comes across as personal interpretaion and I don’t approach it as foundation knowledge but as tinder to spark exploratory perceptions.
Exactly my point. It is personal, and the only thing I could say is if you don’t get the difference between UPG and fact then don’t read it.