It's got a "knife to a gun fight" reference (only involving porcupines) and a [literally] kick-ass heroine, takes digs at Aladdin and The Lord of the Rings -- especially The Two Towers --, the Four Horsepersons of the Apothe...ca...thingamagig make an appearance, and the Librarian is taking a stand -- an important one. (It would be important.)
Also, it's safe to say that by book 5, Pratchett had found his Discworld legs once and for all.