I'm starting to really wonder whether it's worth reviewing Discworld books. "Yes, it's by Terry Pratchett. Yes, it's funny, interesting, and surprisingly thoughtful. The End." It seems like a shame to punish success, though, so I'll explicitly note that "The Last Continent" is yet another excellent entry in the ever-expanding universe that is the Discworld.
TLC is another Rincewind book. There is a definite pattern in all of these books, which follow the same basic plot: Rincewind is brought to a foreign Discworld land which has amazing similarities with a corresponding region on Earth, is encouraged to do something heroic, spends most of the novel running away from anything resembling heroism, somehow survives incredible peril, and eventually saves the day. In this particular entry, the foreign land is Australia - er, XXXX. It is a place filled with friendly people who appreciate a talented outlaw; where they drink beer like water; where most of the land is a parched desert; where kangaroos and other bizarre creatures roam the land.
The main plot is entertaining, and also fairly interesting in structure. There are two primary plot lines in the book: one concerns Rincewind, who was stranded in XXXX at the end of his last adventure, and is tapped by a local deity to fix a wrong that he inadvertently (and anti-temporally) created. The second one focuses on the wizards of Unseen University, who are concerned at a morphic sickness that has struck the Librarian, and who gradually embark on an extended journey in their attempt to restore his health. For most of the novel it is not at all clear what the two stories have to do with one another, but in the end everything is satisfactorily explained.
As to the satirical theme of this book... that's a bit less clear to me. There is an extended riff on the idea of evolution, and mankind's transition to a theory of reproductive biology is dramatically illustrated in a comic scene where the idea is proposed to a creator god. So that's pretty interesting, but it occupies a good, I dunno, 70 pages towards the middle of the book, and doesn't have much to do with the beginning or end. There are some rumbling ideas about aging, and the attitudes generations have towards one another, but these are mostly just tossed off in the middle of a big argument (among the wizards, natch).
On the whole, it doesn't feel like there's a single unified "point" to this book. And you know something - that's okay! Perhaps this is Pratchett's indulgent nod to a romanticized Outback way of life, where people do what they feel like, are interested in what they see, and enjoy things without needing to keep hold of them
Wow... shortest reaction ever! Don't hold it against the book, it's yet another fine bit of craftsmanship from a beloved author. It isn't his fault that he's so consistently good.