Is writing a book series a bad idea?
As is so common with novels, there is usually a string of spinoffs and sequels to go with them. From Harry Potter to Twilight, Percy Jackson to Ender’s Game, all of these franchises have several books and spinoffs in their bookshelf lineup. So what is it about sequels that can make them amazing or make them go horribly, horribly wrong?
First let’s look at a series that I believe to have kept up its quality over its very long lifespan. The Percy Jackson series has survived its initial 5 book Percy Jackson and the Olympians story arc, and is approaching completion of its 5 book half spinoff/half sequel Heroes of Olympus story arc. The series is also joined by two graphic novels, two info books, and a spinoff Egyptian series called the Kane Chronicles. Over all of these books the writing has remained at the same, if not improved, level throughout. What is it that keeps this series going? Rick Riordan has shown that he retains a lot of passion for this series. He is not just doing this because the franchise is popular and he feels obligated to continue. He has a story that he legitimately wants to continue telling, and that shows through his work.
On the other hand is a series that has gone downhill in writing quality over time, through the wild cat adventure series, Warriors. For those that don’t know, Warriors is a series about clans of cats that live in the wild and have to face the challenges of gathering food, defending against other animals, and protecting themselves from each other. This series has been ongoing since 2003, with 5 series spanning 6 books each, 6 independent novels, a field guide, 5 manga adaptations, 6 online-only books, and two spinoff series (Seekers with bears and Survivors with dogs). The series is obviously popular to the extent that it has expanded to such a degree. Unfortunately the quality of writing has declined for all three of the intellectual properties. The problem seems to stem from the way the series is written. The author is Erin Hunter, a pseudonym used originally by three writers and an editor. Over time the writing has been extended to include a group of 6-7 people, all trying to contribute to the work. Unfortunately, this large a group of people makes the writing of all of the series disjointed to a degree. This shows in the decline of the writing near the beginning of the 3rd Warriors series, when 2 of the new writers were hired.
Both of these show how the experience of the writer (or writers, as the case may be) can have a huge effect on the quality of writing over a series.