Feet of Clay

One of the best Watch books imo. Vimes is in rare form, Pratchett's humanism is full-throated, we get some excellent watch-y hijinks, and overall it's just firing on all cylinders. Pretty amazing that this came out the same year as Hogfather, which is also quite good; I think you could argue that this stretch, 1996-1999 or so, is as good as any of the rest of Pratchett's stuff. On the other hand, 2003 had Monstrous Regiment and Tiffany Aching's introduction, which is tough to beat.