Gaiman had the story in his head, but the TV guys kept making him cut bits out because they didn't have time to show them, or because their special effects budget was three and sixpence. He got more and more frustrated with this as production went on, so after the series was finished he wrote the book the way he wanted it. So while the book came second, it's the more authentic version of the story.

But I guess the comment about its episodic nature is fair enough.