Remember when novels were wrapped up in one book? Whether it was To Kill a Mockingbird, Carrie or The Stand, when it ended it well, ended. Do you think series are out of control?
I personally LOVE series. I think it gives the author SO much more room for developing characters and world building. Could you imagine Lord of the Rings in ONE book or ONE movie? Hell no. I think sometimes it's a matter of what the author or publisher decided to do though. Tolkien wanted his book to be in all one volume, but the publisher divided it. The Stand could have easily been broken into 3 books it was so detailed and long. As I work on ideas for my two book ideas I have mixed feelings. The one I can see as a one time novel, but the other I can see as a series of books, much like The Dresden Files by Jim Butcher. I'd like to think it out and outline at least 6 or 7 books, developing characters as they progress.
There are many ways authors do this. J.K. Rowling wrote each book based on a year's time, which worked really well for Hogwarts, and the age group of the kids. Jim Butcher's Dresden books are more of one crisis/bad guy per book and he "solves" the problem by the end. Though poor Dresden is looking worse for the wear isn't he? J.R. Ward has a book for each member of the Black Dagger Brotherhood, and in her new series Fallen Angels has a unique spin on each book, starting with Covet and the second being Crave. I like the idea of each book revolving around a person or a specific event. I think it would make it easier to wrap each one up before going on the next.
Hmmm...just a few thoughts.