This book is the introduction to Kurtz' world of Deryni, and an enjoyable one at that. It can be read as stand alone, or as the introduction to the series, but should be read as the start of the series. "Camber of Culdi" could also be read as the start of the series, but makes a slightly less effective start.
It is the familiarity of the setting that makes it comfortable. Gwynned is clearly quite similar to the slightly more Celtic areas of medevial Britian, with it's borders of Keldor and Merea as Scotland and Wales. The Deryni, a race of Wizards (it's inherited) add the edge of fantasy that makes the whole of the series facinating and unknown.
Clearly she also studied some parts of the Western Ceremonial traditions of Magick, for while she puts a new spin on them for the sake of fiction, she also makes them quite familiar to anyone who has studied them.
The characters, while three dimensional, aren't too complicated as of yet for this novel, as they are later developed more fully in later novels, but they are not characatures. In all, it was an excellent work.