Another quick thought on the OP's question: the newer book seems intended to replace the old one. The old one feels extremely clunky comparatively. The old version required an extensive knowledge of d20, and then how to bend or change those rules for this system. It was trying to force something that didn't quite fit, and it shows.
By contrast, the new system seems more like it was built with the setting in mind, and so it is much better suited to the setting. It is extremely light (although as some have said, there can be quite a bit of depth if you want it) and you can easily explain pretty much everything someone needs to know in a few minutes. The fact that the character sheet is just one page should be a great sign.
And as others have pointed out, the new, thick book is chock full of content. A little less than half introduces the world and how to make a character and play in it - effectively a "players' handbook" - and the rest for the narrator's use - effectively a "DM's guide" and "monster manual." I sincerely doubt - especially 2 years later - that any other supplements will arrive for this system, but as others have said, this book is really all you need.