This is Book 1 of The King Raven Trilogy.
Kudos to Stephen Lawhead for taking yet another worn-out legend and breathing brand new life into it. The concept of making an English Robin Hood into the Welsh Rhi Bran y Hud works incredibly well and it makes for interesting, engaging, and fast-paced reading.
As the opening book of the trilogy, this book strikes a good balance between character introduction and conflict. The internal politics of the time are slightly difficult to keep straight (there are a lot of kings, dukes, barons, counts, knights, priests, abbots, bishops, etc to keep up with) and Lawhead does a masterful job of laying bare the social and political trials for the people of this time.
To better understand the context of this era, I would recommend reading the Author's Note "Robin Hood in Wales?" located at the back of the book before you read the book itself. This will not provide any spoilers for the book itself, and will help you to better understand the context of the political and cultural implications of all that the book contains.
While Christian themes are present in this book as well, they are not as prominently displayed in this series as they were in Lawhead's previous works such as The Pendragon Cycle or The Song of Albion Trilogy.
I thoroughly enjoyed this book and quickly moved on to the next one. I cannot recommend it enough.