Raising Steam takes one of the Discworld plot lines that I have tended to find less successful - some aspect of modern culture intruding into the fantasy environment, as in Moving Pictures, Soul Music and Going Postal - and really does something quite interesting. There's lots here, the major plot line being the mutual interlocking of the Patrician's statecraft with the new technology, and how this affects a power struggle between the fundamentalists and pragmatists among the Dwarves, but there are plenty of shout-outs to characters and situations from earlier volumes. I liked it.
Once you have invented railway trains, society and economics on Discworld are surely going to be altered for ever; and I wonder if Pratchett now feels at liberty to change his creation so fundamentally because he feels he may be nearing the end of his own engagement with it. We started from a parody of Lankhmar three decades ago, and now appear likely to end with steampunk, after many diversions along the way. Hopefully there will a few more stops before the end of the journey.