It's got dated language, idealised versions of the characters whose lives I know better now, and Katherine, though one of my favourite Medieval women, is not actually a favourite character of mine in this fiction, or any fiction. But this book sits in my heart eternally, regardless.
I don't care what is true or not - the richness of the Middle Ages, the nuances, the customs and of course the people, are woven into a timeless tale of duty, betrayal, and love, all the stuff necessary for epic romance. But because there are so many other things in this book besides the romance, and the world contained within is vibrant and raw, dashing and courteous. It's not surprising that Kettlethorpe, Katherine's historical home, was visited so much after the publication of this book (and well after, I've been there myself!), and likely Lincoln Cathedral saw a bit of a surge (Katherine got married to John and is buried there) though it holds its own pretty well.
I really don't need to write a long review, there are plenty of great ones on this page, but what I will say is the book is important because it brought to life a much maligned and little known or understood historical woman and got people interested in her. It probably helped create the surge of interest in other historical women too, and the great thing about that is, though it's fiction,it encourages people to go out and learn more and create their own. Katherine Roet/Swynford/Plantagent was an amazing lady. This is the highest honour she could receive, to live on even after dying in 1403.
And John of Gaunt was hot. He was known as the Great Fornicator you know.