Pratchett's first Discworld novel, The Colour of Magic, was a hillarious send-up of pulp fantasy classics. As the years have gone on, and the heap of Discworld books has towered ever higher, Pratchett has gotten less completely light-hearted, and Monstrous Regiment continues this trend. I don't object to this in and of itself, but I find he can become a bit heavy-handed in the occasional paragraph of editorial commentary.
Having served for a couple of years in the CF Comms Reserve, I appreciate the spoofing of military life and the relationship between officers and NCMs. Things get a bit far-fetched around the relationship between men and women, and while this is done for comedic effect, I found that it stretched a bit thin towards the end of the book. A major plus (or at least a lieutenant or captain plus) of this book was that he introduced a group of new characters to the world. His established characters tend to become somewhat like set-pieces in my view, and without new players, the action can be a bit too predictable.
Before closing, a word of warning to potential readers: this book touches on the theme of child abuse.
Despite its failings, Monstrous Regiment is still a fun book, and one which makes some trenchant obervations along the way.