I like the details Penman adds to her novels; it's obvious that she's taken the time to really dig into the sources (and in fact she quotes from several contemporary chronicles throughout the book), and her author's note at the end does a great job of outlining the (reasonable) liberties she took in writing the book.
Aside from just a few points where I thought there was a bit too much historical exposition stuffed into the dialogue, with characters explaining things to each other that they'd likely not have had cause to do, this made for a good story and an extremely enjoyable read.