I am also a fan of Phillipa Gregory's portrayal of the Tudor rein, and the Tudor TV series. A.E. Moorat stuck very close to history (other than the werewolves and supernatural creatures!), which made the story even more compelling. If Henry VIII really was a werewolf, it would explain a lot!
It's obviously not a literary piece. It was extremely fun, gory, ridiculous in its own way, but you take it for what it is. To read it, I would suggest that you have to be familiar with the history. The book seems to assume that you know who the main characters are - there is no character development, except to develop the characters into their supernatural roles!
Henry Tudor being a werewolf explains his extremes, his weight, his bloodlust, his temper, and his lust. The book also introduces a religious sect of supernatural slayers, of which Jane Seymour is one. (It would be really interesting to have the sequel to this book and have Jane Seymour's as a Protektor on the lycan king.
The characters that were the most fun were completely fictional - a false witchfinder, Hob, and his bloodthirsty psychopath wife, the hag Agatha.
It really is a must-read book, for anyone travelling on a long flight, or who has a rainy weekend to pass in bed. Have some fun, be open-minded, and leave the criticism for the literary works.