Like Thud, The Fifth Elephant is a discworld novel that centers around commander Sam Vimes and the watch (the Ankh Morpork police force). In The Fifth Elephant, Sam Vimes is sent on a diplomatic mission upon which he must ensure that the new "low king" of the dwarves is crowned and save the foreign city from usurpation by an "old-school" werewolf.
Although the book is entertaining and humorous, I did not enjoy it as much as I did Thud. As I mentioned in that review, perhaps it's the reading (I listed to an audio recording) that made Thud so enjoyable. I would recommend Pratchett to someone looking for some light reading. He does provide some insight into human behavior and the dialogue and writing often contains puns and other humor. I don't count myself a Pratchett-fanatic (though I think there are some die-hard fans out there), but I've enjoyed what I've read of his.