This series is absolutely one of the fantasy genre's treasures! It's wonderfully light-hearted and humorous; the author revels in puncturing any number of fairy-tale conventions. Princess Cimorene, for instance, isn't kidnapped and enslaved by a dragon --she voluntarily becomes housekeeper for the Dragon King to escape an arranged marriage. (And the draconian king is female; dragons use that title for monarchs of either gender to keep things "simple.") But though her main characters often don't do the conventionally "proper" thing, they always try to do the genuinely right thing.
Practicing Roman Catholic Wrede [pronounced "Reedy":] writes good clean fantasy (both serious and humorous), free of bad language, unwholesome sexual content, or gratuitous violence. (Here, for instance, Cimorene and her cohorts deal with dastardly wizards simply by melting them into goo with soap and water, like the Wicked Witch of the West in The Wizard of Oz --but they always eventually regenerate.) Her work is informed by an equalitarian feminism, in the best sense of the word, which is not at all anti-male. IMO, she's one of the very best fantasy writers of our generation. Readers who like this series should explore her other work; I can personally recommend The Book of Enchantments and Caught in Crystal.