British sci-fi magazine SFX (in issue #88) recently published a short interview with screenwriter and frequent Alex Proyas collaborator Stuart Hazeldine.  

We obviously can't publish the whole interview here, so we'll summarize and use some snippets.

- Hazeldine had only a "vague knowledge" of the novels before starting the project.

- he thought it was "one of the best concepts for a long-running sci-fi TV show" that he'd ever heard of, and believes that Riverworld could be destined for greatness...he can see it as the Star Trek of the 21st Century.

- Hazeldine wrote his first draft of the screenplay based entirely on Alex Proyas's treatment, so he would have no creative limitations.  After reading the first two books, he found that most of his ideas were pretty accurate, but "significant work did need doing."  

- he felt that "some of the stuff in the novels felt dated and needed contemporizing."

- he decided that Farmer's narrative tended to bog down in the face of the magnitude of his ideas and concepts.  Hazeldine felt that his job was to construct a strong story within the framework of the established premise.  

- he has come up with "a lot of stuff that riffs off Farmer's explanations" that Executive Producer Proyas apparently likes.   

- Hazeldine had to know how the story ends in order to begin writing it.  In order to keep the mystery to fans of the books, he has changed some events, especially in the end, while maintaining respect for Farmer's own choices.   

- interview also revealed that there are, indeed, eight main characters and that three of them are invented by Hazeldine (these characters are probably Valdemar, The Polish Jew and the male lead, Jeff Hale).

Special thanks to Zacharias L.A. Nuninga, from the Philip Jose Farmer - International Bibliography