I do one Xanth novel a year, because at the moment that is all that publishers will accept; they don`t want any other type of fiction from me, so Xanth pays my way.
I did not know at first that it would be a series; I discovered after the first novel that I had more to say about it, so I did another. And another, and then the readers demanded yet more.
Douglas Adams` Hitchhiker series also shows the potential of lighter fantastic fiction. I read the first, and listened to a tape of a later one, and it`s fun.