This one really reads as a medieval romance. Not so much because of the (moderately) archaic language but because the characters think, feel and behave very differently from us moderns.
Unquestioning belief in magic (anything supernatural really) combines with absolutely no curiosity as to how and why it works, to the point that when the heroine comes to eponymous Wondrous Isles and finds each one differently strange, she does not try or even want to find out anything about their nature, just wanders around hoping for something that may help in her quest.
And yes, the Quest theme is of course much in use to this day, but here it is also worked in medieval fashion, trusting to fate and not thinking it over from all sides.
Little reflection is another trait common to the characters, and I don't mean it in the negative. When a decision is taken, they don't waste time reflecting, just go ahead and do it, however dangerous the path or uncertain the result.
All in all, this is a fairy tale, but it's not sugary and pink, and the characters are not one-sided. Oh, and most important of them are women, including the protagonist, which does not hurt the romance one bit.