Terry Pratchett's fortieth Discworld novel tackles many of the author's favorite themes, the heart of which can be found in one of his quotations: "It was funny how people were people everywhere you went, even if the people concerned weren't the people the people who made up the phrase 'people are people everywhere' had traditionally thought of as people." Part of what makes Pratchett a great writer is how well he does people: human people, dwarf people, troll people, goblin people, golem people...they're all people. They're all frightened-clever-ambitious-earnest-conniving-brave-opportunistic-caring people.
The last thirty years and forty novels have brought Discworld from a (literally) flat parody of sword and sorcery novels to a nuanced exploration of human nature and any number of issues therein. This one is partly about the continuing modernization of the world—in the form of the invention of the steam engine and inception of the railway—and partly about the backlash against any kind of change—in the form of traditional dwarfs taking up terrorism and plotting a coup because the world is changing in ways they can't control. Moist von Lipwig is taken from his position as the head of the Post Office, the Bank, and the Mint, in order to take charge of this new project and get it rolling. As can be expected, the book is by turns funny and poignant, the insights very insightful, and the silliness rampant.
Why, then, do I feel rather lackluster towards the book as a whole? I suspect it's because after thirty years and forty novels, we're just retreading the same ground, merely phrased a bit differently. Jingo dealt with war, innovation, and the ridicule of pervasive ethnic stereotypes, any number of books have dealt with humanizing the "alien" (Feet of Clay, Snuff, and Thud! to name a few), and the vagaries of politics have been explored in virtually every novel containing The Patrician of Ankh-Morpork—going all the way back to the very first book, The Color of Magic, which has all the depth and complexity of a pre-schooler's woodblock puzzle. Then, of course, is the tour of Discworld's greatest hits, featuring a cameo by Queen Keli of Sto Lat, partly starring the son of the man who made the first combine harvester, brief appearances by the faculty of Unseen University, a fly-by visit from a History Monk, and allusions to strange forces which control themselves with minimal support.
If you have not read any Discworld novels, don't start with this one: there's far too much to absorb. If you've not read all of the Discworld novels, you'll be very pleased with this one. If you have read them all, you can still enjoy picking out the parts and calling back to where you've seen them before. Is this one of his greatest? No. Is it still worth reading? Yes, very much so.