If you're a fan of Sir Terry Pratchett's Discworld -- go read Raising Steam. Really there's no more to be said.
If you've not read a Discworld book, this isn't the place to start. This is a book that comfortably assumes our familiarity with many of the characters and there is a REAL pleasure in learning more about them, watching them behave as who they are and yet reveal new aspects. The little character reveals are wonderful - and there's one at the end that just plain delighted me.
I'm trying not to share any spoilers and it's difficult. The book is so well-constructed that I want to say "did you see XXX coming?" or "wasn't it perfect when?" or "didn't you adore Flash?"
If you're looking to dive into the Discworld, the series order is here. For me, the true magic of the books begins with Wyrd Sisters, but if you want to read the city of Ankh-Morpork set books, start with Guards, Guards. Unless, of course, you're scared of dragons ;)
Terry Pratchett plays with words. He isn't ashamed to pun - especially in footnotes. His style is witty, critical and compassionate. Some reviewers have noted more serious, sombre elements in his later novels, but I think they were there earlier. He has something to say, and he says it with laughter and hope. Raising Steam is wonderful.