Actually, after reviewing Armageddon's Children, I remember a conversation I had with Heather. I am a fan of Terry Brooks and have read almost all of his books. The conversation was on the dilemma that authors face in writing a book series.
Say an author writes a book, Book 1. That book is popular and the public clamors for more. The author writes Book 2 as a sequel. Then maybe the author writes Book 3 as another sequel. Book 2 and Book 3 will never make as much in sales as Book 1. Why? Most people will want to read Book 1 before reading Books 2 or 3. A few people won't like Book 1 and not bother to buy Books 2 and 3. Therefore, the returns on the books are smaller.
An author like Terry Brooks knows this. In his Shannara series, he has tried to renew interest by having new sub-series. The first of these after the original Shannara series was quite successful. The trilogy after that (the Voyage of the Jerle Shannara) was somewhat less so. The most recent trilogy (the High Druid of Shannara) was rather boring. Again, he's writing towards a diminishing audience. There are definitely people who may want to read the later books, but I would think that it actually pushes up sales towards the first book, the Sword of Shannara as well.
So Brooks, and other authors, try to expand their repertoire. Brooks wrote a prequel to the Sword of Shannara (Book 0 if you will). But then he wrote the Kingdom of Landover series, a separate grouping of 5 books completely unrelated to Shannara. As aside, previously we knew that they were completely related. However, the main character in the Landover books arrives through a portal from Earth and the characters have in the past traveled to and from Earth. Could it be that they are interconnected after all? Only time will tell.
Anyway, Brooks then wrote the Word and Void series, based here on earth in the 1990s. Again, this was (at the time) different from the Shannara series. Thus, it provided a new entry point for potential readers to pick up and read a Terry Brooks book. Armageddon's Children was supposed to be a similar entry point as well; if you read my previous review, you'll see that I disagree with that assessment.
So Terry Brooks has published 25 books. Two of these, Hook and Star Wars, The Phantom Menace, were novelizations from movies, so I really don't think they count. Of the remaining 23 books, five are in the standalone Kingdom of Landover series, which has an entry book, "Magic Kingdom For Sale -- SOLD!". For the remaining 18 books, there are only three "entry points" to the series: The Sword of Shannara (Book 1 of my example), First King of Shannara (Book 0 of my example; as a prequel it could be used to introduce the entire series), and Running with the Demon, the first of the Word and Void series.
I think you can easily see the difficulty here. Out of 23 books, there are only four entry points. Even worse would be Harry Potter; of seven books there is only one entry point. Compare this to an author who publishes more stand alone books, such as John Grisham, John Irving, or Steven King. Each book is self-contained. Any of them can be picked up by anyone at any time, with no reason to read them in the order published. Potentially, a lot more money can be made by writing like that. However, each story set would be much smaller. If you've gone through all of the trouble creating an imaginary world, you want to use it as much as possible.
Having said all of this, I am pleased with the effort of Terry Brooks to introduce Armageddon's Children as a new starting off point (even if it isn't). More readers equal more profits meaning more books. I just wonder about the economics of writing series versus stand alone books.
Quick thoughts to wrap this; compare this to movies or computer games. It seems that half of the new releases out there are sequels to previously released material. Maybe it's just harder to constantly invent new worlds? Maybe audiences are more comfortable with stuff that they know they will like? I guess I just have difficulty understand why there are so many sequels when you're constantly battling diminishing returns...