It’s definitely better to endure a long wait and have a quality sequel, or no sequel, than have a bad sequel. A bad sequel can spoil the books that came before. A good sequel after a long wait enhances the previous books. No sequel, whether because the author died or lost interest in the series isn’t ideal, but it doesn’t spoil anything.
There’s something about an unfinished series that people like. When you have a finished series, it’s like a whole book. It’s longer, but it’s the same emotional experience, it’s complete, over. An unfinished series on the other hand is much more likely to provoke conversation, because you’re wondering what will happen, and whether the clues you have spotted are clues or red herrings.
The final volume of a series closes everything down. With luck, it closes it down in a satisfying way. But even the best end will convey a strong sense of everything being over. An ongoing series remains perpetually open.Some people find it off putting to discover that a book is part of a long series. Other people are delighted—if they like it, there’s so much more to discover. Reading unfinished series gives you something to look forward to.”