I have a peculiar quirk as a reader: except in the case of nail-biting, gasp-worthy cliff-hangers, when I finish a book in a series, I don't immediately reach for the next. Instead, I reach for another author, often something as different as possible. It may be (in fact, usually is) months before I meander back for book #2 or #3. This is nothing against the books: I do this even with authors I adore. After deep immersion and acquaintance with a world and group of characters, I feel the need for new fictional surroundings.
This tendency filters into my writing as well. While most of my novels leave threads untied and possibilities open for future volumes, I typically don't feel the need to start working on those. I don't have many story sets, where multiple short stories involve the same world or characters - probably my longest arc is the Ishene and Kemel stories, and those were written out of sequence. The new path to a major publisher which has sometimes been touted - write short stories in the setting, get them published in pro magazines / anthologies, then write a novel - pretty much seems like a nightmare to me. I feel for every author who's said they're tired of writing "another X novel."
I need variety - I need to periodically switch it up and do something different. It's why I'm typically working on two or three projects at once, but of different sorts or in different stages. Right now, that's writing Unnatural Causes - a high fantasy mystery / intrigue novel with a sometimes snarky non-human first person narrator - and editing Who Wants To Be A Hero? - a humorous fantasy novel involving multiple narrator viewpoints and a mix of third person and first. I'm also pondering tackling my zombie novella. I have what I hope is an unusual take on the idea, and it's so athwart what I usually do that I thought it would be a fun escape.
And isn't that what reading and writing are about - escape from the normal?