The Warlord Chronicles are among my favourite books, having read them a number of times. Whilst this adaptation captures some of the key elements of the first book, there is still much that is missing, particularly a heart to the story.
This is made to be Arthur's story rather than Derfel's. Consequently the complexities and nuances of certain relationships between characters are lost, particularly through the role of Merlin. This makes the production less interesting than it could otherwise have been.
World building is also a bit lacklustre and the sense of scale is lost by putting characters on horseback, a very noticeable shift in the story. Thus we lose some of the grit and realism of battles that came through the book (where are the shield walls?) and could have made for a compelling adaptation, rather just giving us something that we've seen before.
The adaptation also seeks to reflect "the world we live in today" through both its casting choices and the way in which certain characters are written. This works in some respects, but doesn't in others which is ultimately to the detriment of the show.
I've watched through the whole of series 1 and whilst I found it watchable, as a long time fan of the books, i felt this was an opportunity missed.