Note from the Reviewing Trenches

There is a difference between what you can get away with in a serialized story (comics, tv shows, multipart fanfics) and a series (books, graphic novels, movies). There is a difference.

You need some kind of completion from a unit in a series. You may have written the first book of twelve in King of the Steampunk Superhero Bears, but while you can leave all kinds of things up in the air for the next book - Where the lost chess automaton of Jinae is, whether or not Bobilith and Betsy will ever kiss, who will be the new King of the Steampunk Superhero Bears - you need to resolve something. The vanquishing of The Otter Queen of Quipao, Betsy and Vermillion turning from friends to enemies, some kind of storyline needs to be resolved in a satisfying or at least substantial fashion.

Because if someone has to wait another year and pay another $16 to find out where anything is going? Chances are they won't.

And don't tell me your trilogy/quadrology/whatever is just really one long story. Lord of the Rings ended its first book with the tearful conclusion of the Boromir arc. Pawn of Prophecy - the first part of FIVE! - ends with Garion discovering the full truth of his heritage and the fact that contrary to mythic stereotype (the only time Eddings broke from it, but whatever) his family really is his real family. Even the flipping Phantom Menace ended with a celebration of "victory" on Naboo with Palpatine rubbing his hands in foreshadowing evil glee. If George Lucas has figured it out,  you can too.

It's tempting to think like a serialized storyteller and end with Bobilith jumping off a cliff about to live or die, having done nothing but introduce the characters and settting, but if you're not a tv show or comic book, you can't act like one. If people have to wait a long time and remember to go out and spend more than the cost of a nice lunch to get your next installment, newsflash, you're playing by different rules.

Don't let your reader or viewer walk away saying "What was the point of that?", give them something for their time or money, and send them home satisfied. Don't be the dinner party that causes people to stop at McDonalds afterwards because they're still hungry.

So yes, unidentified authors whose books are not commercially available yet, I didn't give you glowing reviews. Sorry, bucko. 

And by the way, if you end your series with "Rocks fall, everyone abruptly dies, except for the morally repugnant ones, here have two chapters of them being smug and happy in the future, no plots will be resolved because they're all dead" you may have conned me into paying for all of this series? But good luck getting me to pay for the next one. I'm looking at YOU, Jennifer Fallon.

ETA: I'd love to hear your personal unfavorites or anecdotes about this sort of nonsense!