This foray into the Discworld starts off sounding like a travelogue, where the witches Granny Weatherwax, Nanny Ogg, and poor, put-upon Magrat do the typical touristy thing. The latter half, however, is full of the observations of human nature that make Pratchett so worthwhile.
For example, there's the note that happiness can't be imposed from the outside, with a fairytale city where the streets are too clean and the people too cowed. The fact that this city is imposed on the Discworld's version of New Orleans gives it that twist that sparks the interest, including a full-flavored Mardi Gras, alligator sandwiches ("and be quick about it!") and marvelous gumbo. And even a version of Baron Samendi (and a reference to the voudon god Red-Eyed Erzulie.)
But most importantly, the book centers on a discussion of what it means to be good, which, as Granny Weatherwax puts it, is "giving people what they need, instead of what they think they want." And because of this, she has to fight the story that wants to happen, the rural myth that the beautiful girl goes to the ball and marries the prince. And she has to fight the woman who set the whole thing in motion, someone Esme Weatherwax knows from long ago.
Hopefully, the pumpkins will come in handy.