Women in leadership
This book was controversial at its time, for the opposite reason it would be controversial today if it were published. Some of this book would strike the reader as potentially offensive because it often casts women in a secondary role, but in his time, it was regarded as highly progressive. It framed arguments about female competence by using cultural evidence about powerful women in leadership, of which there have been many. By telling their stories, he is offering a new narrative about women, that they might be naturally competent and able, just as men.
Women as divine agents
Boccaccio heralds women in many of these accounts, using the mythology of the earth as a warrant for this argument, that women are equally able to be agents of the divine. In mythological terms, perhaps he is seeing women as heroes in their own rite. It certainly feels that from his telling of the stories of Isis, Cleopatra, and Dido and more, that he views women as participants in some kind of "godlike" experience of reality. He comments frequently about Greek, Roman, and Egyptian goddesses.
Gender and morality
This author is a product of his times, so perhaps a modern reader will see far past his conclusions, but at the time, the book was received as controversial because it shines such a powerful light on women. Indeed, it was the first book to be published that was specifically concerned with women as its subject. With that being said, he sees gender as a platform for morality. The way he sees it, women are unique from men, morally speaking. He notices that in Eve's story, her sin was being willing to entertain licentious suggestions, because of her desire. Although Adam's sin is literally identical, Boccaccio feels that women more closely embody thematic tendencies toward deception and lies.