I thought Red Knight was great. In particular, his magic system was original and well-developed. It reminded me slightly of Jordan's Tel’aran’rhiod in the Wheel of Time series but was very different and not derivative. Also, his battle scenes with medieval arms and armor were particularly realistic, since he is very active in the re-enactor movement and actually knows what it feels like to wear armor and use medieval weaponry.
The second book in the series, The Fell Sword,
http://www.amazon.com/Fell-Sword-Tra...rds=red+knight, has recently been released and was also good but I didn't like it quite as well as Red Knight.
I haven't read any of his historical fiction, written as Christian Cameron, but he has quite a following and has a great website with a very active fan base and a forum, Online Agora, which has a lot of lively discussion.