Long series run into some problems, particularly if they’re a single, ongoing story rather than a sequence of episodes. Robert Jordan ran into some of these problems, as has George R. R. Martin. I think much of it can be mitigated by releasing books regularly. The Wheel of Time reads much differently to me now that I know the ending, and am not waiting years between books, only to get one that doesn’t feel like it progresses the story as far as I want. I have an advantage over people like Robert Jordan and George R. R. Martin in that I’ve read Robert Jordan and George R .R. Martin. They’ve had to do this without examples to follow. What I have going for me is that I’ve been able to watch them do it, watch them hit those pitfalls (and admirably do great jobs of crossing them), and hopefully learn from their example.
I feel the other big danger with the long series is the explosion of side characters. Sometimes, it seems that their narratives–and their plots–take the bulk of books, causing some bloat to the series.
I can’t promise my writing won’t deteriorate. I haven’t ever tried something of this length before. However, I have attempted, in the Stormlight Archive, to do some things to try to forestall it. Specifically, I’ve outlined quite a lot. I know where I’m going.
Tangents will be kept to a minimum. I’ve given myself the interludes, as I’ve mentioned before, to let me explore some tangents. I think this will keep me from feeling I need to tell entire books about side characters; I can give them an interlude, and hint at a greater story for them. Then I can leave them be.
The other thing I’m doing has to do with the flashbacks. Each book will have a single focus character, and I will delve into their backstory. I’m hoping this will give each volume it’s own cohesion; rather than just a tiny slice of a story, I hope this will help make each one feel like it is its own story.
Time will tell if I succeed or not. Until then, I don’t fault you for being wary.