I love Sam Vimes, pardon me, His Grace, The Duke of Ankh, Commander Sir Samuel Vimes. And I love the development of the character from 'Guards!Guards!' to 'The Fifth Elephant' and further. And this book offers a possibility to recall it all over again in a new way.
Recommended only to those who read the Watch Cycle before.
Probably not a good introduction to Pratchett for the casual reader, since so much of the story's impact comes from its place in the overall Discworld series and the prior arc of Vimes stories, but definitely one of the most satisfying novels he's ever produced.