Being Australian, I was a little worried that non-Australians might not get many of the Aussie-themed jokes and cultural references -- fortunately, this seems not to be the case. (Although, having met Terry at a book-signing for "Last Continent", he was at pains to find out if I had picked up all of the Oz-references, and was delighted that I had, so he obviously took a great deal of care and did much research for them).
Last Continent is an interesting mix of Pratchett's usual style, with slightly more characters and slightly fewer clear plot points than normal. As a result, there is less of a "story" to follow but more fun people and more scope for one-liners. I found it slightly less enjoyable than, say, "Hogfather" (roughly of the order of "Jingo", which had more of a moral and political tinge to it) but still a very fun read.
Readers new to Pratchett should probably read the other Rincewind books (particularly "Colour of Magic" and "Light Fantastic") to get a feel for the main characters, as knowledge of their personalities adds a great deal to the enjoyment of this book. Reading it cold would probably give a bit of a distorted feel for the series. And remember, if RIncewind is not your bag (baby), there's always the Guards series (my favourite -- try "Small Gods") or the witches (try "Equal Rites").