Monstrous Regiment is not one of the best Discworld books, I'd argue. It shows Pratchett's personal politics more than other books, and its final character arc is so cheesy it's downright embarassing. That said, it stands among my five-star books because it was (and possibly is) tremendously important to me and I can't get it out of my head. Also, props for accurate depiction of what eastern Europe is like.