Perhaps this has happened to you. You’re reading a book, you’re interested in the characters, the plot is carrying you along, and you’re really looking forward to seeing how it’s all going to work out, especially as complications ensue and twists occur and you’re looking at the amount of the book left to read and it’s getting shorter and shorter. You reach the end, and only then discover that no, the author isn’t going to resolve the plot in this book because there’s a sequel! There was nothing in the publicity or the reviews for the book, and nothing in the book itself that indicated this wasn’t a stand-alone book, so you feel doubly gypped.
That’s happened to me a few times, most recently with Once and Future, by Amy Rose Capetta and Cori McCarthy, and when it happens, whatever good feelings I had about the book drop dramatically when I discover that the author(s) pulled that kind of trick on me. My feeling is that readers and authors enter into a sort of implied agreement : the author is going to play fair, not pulling solutions to plots out of thin air, not violating the rules the author has set up for this particular universe, and finishing the story by the end of the book. If the author is not going to finish the plot in one book, I feel it’s only fair to let the reader know in advance, by indicating somewhere that this is the first book in a series. Leaving the reader to find that out in the last pages of the book feels like a violation of that author-reader agreement.
It’s not that I don’t like books in series, or that I don’t understand that sometimes a story is too long and too complicated to be told in one book. I’m perfectly happy to read a book that’s part of a series, as long as I know it’s part of a series when I start, so I can decide if I want to read the first part now and wait years for the next part or not.
It’s possible, too, for a book to be part of a series and yet tell a complete story in itself. For instance, there is a several book arc in Jo Nesbo’s Harry Hole series in which a wrong done in the first book finally gets righted, but in each one of these books, the main plot line is resolved, even if those other issues are left for a later book to resolve. In the same way, Felix Palma’s Map books (The Map of Time, The Map of the Sky, The Map of Chaos) are obviously all connected, and it’s much more fun to read the later ones if you’ve read the earlier ones, but each book resolves (and in each case the resolution is both surprising and perfectly reasonable, given things that happened earlier in the book), and none of them leaves you hanging and waiting for a sequel to find out what happened to the characters. The more I think about series I have enjoyed in the past (including Lev Grossman’s The Magicians, The Magician King, The Magician’s Land, and Hilary Mantel’s still unfinished series about Oliver Cromwell, Wolf Hall and Bring Up the Bodies), the clearer it is that I have no problem with a series as long as each book in the series is self-contained.
Nor do I have a problem with a series where the story is continued over a couple of volumes (I grew up on The Lord of the Rings, after all), when I know from the outset that book one is not going to answer all the questions it raises. It’s about expectations, really. My expectations may be unreasonable (I don’t think they are, but then, who thinks they’re being unreasonable?), but if you want to make me happy as a reader, play fair and tell me at the outset whether you’re going to tell the whole story in one book or keep me on tenterhooks till you get the next book published.