I like series. If I’ve enjoyed a book (or movie or comic) I’m happy to know there’s a sequel and look to get my paws on it. I’ve made the investment in the characters and a sequel feels like a return on the investment.
Bad sequels are bad returns. And if I’ve read the first book of a series and I don’t like it I do feel some relief at not having to go any further. All those pages, all that commitment of time and concentration, that I don’t have to feel pressure to get with.
When the book is part of a yet-to-be-completed story, I’ve learned (big surprise) that, if there is a long interval between what I last read and the new installment, I forget. Who are these people? What are they doing?
L. Frank Baum, when writing his Oz books, seemed himself to forget what he’d said in earlier Oz books. In one book the Magic Belt can easily be commanded to do all sorts of amazing things. In another you can only use the Magic Belt on alternate Thursdays while standing on your head and whispering a goofy rhyme (or something). In one book Oz has no money. In another kids are buying lemonade with green pennies.
I didn’t start the Harry Potter books until the third had been published. Now when I read a new one I have to work my little brain to remember whether a particular character is one who’s appeared before or not. How many Weasleys are there again?
It’s easier on my creaky memory to read a series all at once (or with brief breaks) than to wait a year or more between episodes.