Having read all of Phillipa Gregory's books on the Lancasters, Yorks and Tudors and having seen other adaptations of her work, I knew that this would be good entertainment even though it is rife with historical inaccuracies.
Being Gregory is a historian, I find her penchant for deviating from history as well as just making things up extremely distressing and annoying. The actual history is compelling enough and in no need of elaboration. People will read her books and watch her movies thinking them to be accurate.
So if you want good entertainment this is a good show. The casting is excellent, the costuming is fabulous and in general this is a very well made show. Just realize that it is not history but very loosely based on history.