Books are so much about personal taste. I think I can see why this has so many positive reviews and William Marshall is a wonderful historical character to write about but...
I'm inclined to follow my heart and say, I prefer my stories to be based on myths and legends, rather than reading the words an author chooses to give a character. Somehow, I am distracted by the fact that the events might be real but can we really believe what he thinks and feels at the time? And how much do we really need to know about medieval this and that - my imagination does the work so the author doesn't have to! I much prefer books such as Lancelot And The Wolf
and Lancelot and the Sword for that reason, along with Achilles. Fast paced, imaginative and with just enough historical background I saw the world without becoming bogged down. They gave me the freedom to roam in my own version of Camelot or Tory.
This is well researched and well written, but not for those who like a little fantasy with their medieval heroes.