Shared world has done some world building and brings (in the case of FR and SW) a big audience. With your own work, you're more creatively free. In a way, the shared world stuff has a high floor but a ceiling.
Paul S. KempThe Forgotten Realms is arguable the most detailed, intricate fantasy setting ever created this side of Middle Earth. It's a setting for many D&D game products and lots of fiction. It is vast, historically and geographically and so contains just about anything you might imagine, at one place or time or another. Created by Ed Greenwood. And, for the record, Ed Greenwood is one of the smartest guys I've ever met.
Paul S. KempOriginal work has no floor and no ceiling. You can reach essentially zero readers or millions.
Paul S. KempI try to pester Christian Dunn from time to time. As soon as my schedule allows, I plan to make a real pest of myself and get some hot, slippery Chaos action.
Paul S. Kemp