This book is the first volume in what I consider to be arguably one of the best series of all time. It's got it all: politics, violence, sex, intrigue, psychic powers, comedy, epic storylines, fascinating characters, anthropology, mythology, several other -ologies! Julian May takes standard elements of fantasy lit (long journeys, strange mystical creatures, a quest for some special artifact, etc.) and combines them effortlessly with standard science fiction stuff (aliens, galactic civilizations, etc.). I've never seen anyone do so with such pleasing results. I've read Many-Colored Land and its sequels many times over the years and they just get better with repetition.
In regards to this volume specifically, it starts out kind of slow, but picks up once the main characters translate through time from early 22nd Century Earth to the Pliocene Era, 6 million years in the past. Part of this stems from the fact that it was written as one book with the second volume, The Golden Torc, and was then split by the publisher. The two books should be read as if they were one and they'll flow much better.
Read this book! Then read the others! You will not regret it.