From what I've heard RTD had the idea for CoE just sitting around so he took it and used Torchwood to tell the story (it would have worked better if they had used other characters) and he wrote the characters to fit the story instead of writing the story to fit the characters.

This makes sense, because by the third epi I was wondering who the hell were these people? On the other hand, the idea was at best half-baked. I'm starting to wonder how did he earn that genius label everyone throws around...