As a novel, Terry Pratchett's Hogfather is neither good nor bad. The story of Santa Claus as told in the alternate universe of Discworld is surprisingly conventional in both its plot and its writing. Just as in every other Christmas tale, we find a world without a Santa Claus, and all is restored through the "magic" of belief. The twist is that this story features stabbings and nightmares and the mythical figure of Death (as if there's no such person as Tim Burton). So basically, it's like a Rankin Bass cartoon crossed with The Nightmare Before Christmas (which is basically, The Nightmare Before Christmas).
As an aside, just once I'd to see Christmas saved by cool rationality, skepticism, and a healthy regard for common sense. Alas.
Considering the sometimes satirical tone of voice, Pratchett is neither all that subversive, nor is he very funny. He's no Douglas Adams. Not even Robert Asprin (whose groaningly titled "Myth" books I enjoyed as a kid). He takes a stab at a grand unifying theme, but what's the point of imagination and belief in a world where magic really works and universities are staffed with Wizards?
I was originally attracted to the book because of the TV mini-series and my mistaken belief that it had something to do with the Scottish New Year celebration of Hogmany. The mini-series itself is a charming British hybrid of Harry Potter and Dr. Who: all earnest nonsense, theatrical staginess, and mostly laughable, occasionally impressive, special effects. While their attempt to portray Death with an immobile skull mask and the UK equivalent of James Earl Jones's voice was kind of sad, the actors playing Mr. Teatime and Susan helped the show get through the creakier bits.
All in all it was entertaining enough to sit through, even if the assassination plot goes unfulfilled, we spend way too much time dealing with the Tooth Fairy, it's never explained why the Hogfather has disappeared in the first place or why the Auditors want him dead, and the whole subplot at the University involving the bath tub and Hex the thinking machine is just plain dumb.
What was really strange was how closely the filmmakers were able to follow the book: entire scenes, whole chunks of dialog, editing, pacing, cuts. It's all there. If you've seen only the show, reading the book is like reading a screen play and vice versa. It adds nothing to the telling. It's redundant.
As for Hogmany, I think it has something to do with Vikings, but the book isn't really about that. If anyone does know something about Scottish folklore, I'm sure there's a good novel just waiting to be written.