While discussing the book's genesis, James mentioned Madeleine L'Engle as his chief inspiration, and that influence is certainly evident throughout The Unwritten Girl. In fact, it might be just a little too evident, especially since both the framing story and another story within the narrative have marked similarities to A Wrinkle In Time: geeky, unpopular young heroine sets out to save a family member who has been trapped in a nightmarish alternate world, accompanied by another family member and/or a boy she's just met who seems to be falling in love with her. These and quite a few other elements of the book evoke L'Engle, to the point where it passes beyond affectionate homage and starts to seem, well, a wee bit derivative.
That's not to say that The Unwritten Girl is just a thinly veiled retelling of A Wrinkle in Time, though, because it isn't. James also draws from a number of other fictional wells: indeed, in some respects the plot reminded me more of Edward Eager's Knight's Castle, which I wouldn't be surprised to learn James hasn't even read. I also caught echoes of Norton Juster's The Phantom Tollbooth and a few other children's classics. Still, that's perfectly in line with the spirit of the book, which relates the heroine's journey through the Land of Fiction, and thus the reader is intended to find a lot of the settings and characters familiar.
Also, the most effective and engaging concepts in the book seem to be wholly original, so while I could wish that the L'Engle connection had been downplayed a bit more, it would be a mistake to accuse James of lacking his own creative vision. The Sea of Ink, where characters are born, is a fabulous invention, vividly and effectively described; and the idea of the Mystery Man, who is made of clear glass and whose thoughts and motivations must be deduced rather than observed, is nifty enough to be worth the book's price all by itself.
The climax of the story (two climaxes, actually) is terrific, and the resolution satisfying. It's not hard to imagine that some young readers might fall in love with this book and want to read it again and again. So if you have a fantasy-loving child on your Christmas list, you might want to consider buying them a copy of The Unwritten Girl.