The Life and Death of a Series by Christine Amsden
The world is full of series for one simple reason: They make money! Readers who enjoy one story clamor for more – more of the character or of the world, the mystery or the romance. Whatever it is they loved, they want to recapture that feeling in a sequel.
Problem is, people don't always know what's best for them. There is definitely such a thing as too much of a good thing. Some books are better off as stand-alones, even if there are loose threads at the end. When does life ever come to a neat conclusion anyway? Not every secondary character needs a story of his or her own just like we don't really get to know all the people we meet. And as far as I know the world has never come to a neat “happily ever after” – wars come and go, politicians rise and fall, movements ebb and flow.
There are several different types of series, many of which it would probably be more accurate to call serials. A serial is a story that is relayed in installments, so that in actuality you are reading one big story broken into chunks. The Lord of the Rings is a classic example of what I mean. A true series is a collection of closely related stories, but in fiction the term has come to be applied to both types of stories, and to those that fall in the gray area in between.