It's a bit of a shock to find someone who can tell his story in 100 pages flat. Usually it's a trilogy at least. But Hill pulls it off.  Sequels are possible, but I liked it well enough to hope he doesn't. I think of Against the Fall of Night / The City and the Stars (and sequel), 2001:  A Space Odyssey (and sequels), and "With Folded Hands" (expanded into a novel, The Humanoids, with sequel), and hope he doesn't.

Eden is an Ancient Aliens and the Origins of Humanity story, which is not a spoiler, because Hill tells us this in a note at the beginning.  More points to him for not trying to use this used theme as a Big Reveal and Punch Line.

Eden is set in southern Iraq, "northeast of Basra", a "sun-scorched landscape" that is not many people's idea of Eden. Conditions have deteriorated since Adam and Eve. 

"If this is paradise, how bad could hell be?"

"If E.J. and I commit the original sin we could get kicked out of this place and go home?" 

And some of the locals take violent exception to their presence, which drives them into the Mysterious Ruins Uncovered by a Sandstorm. Once inside, they Open the Sarcophagus. That noise is the characters and fans of a thousand movies, telling them Don't Do It! But of course they do, or we wouldn't have a story. 

Hill's speculation, besides "What if it were true?" is that the aliens "were a lot like us."  Certainly their motive for coming to Earth is human enough.  And their behavior towards the natives of Earth is similar to that of countless human imperialists. 

Other referents: Various Star Trek episodes and Haggard's She books. It's not any of these, but they came to mind anyway, in a tangent sort of way.

So: Ancient Aliens invented us and One of Them Is on Our Side. The details of this are the story, so I won't spill it here.  Few of the separate elements are all that new, but on the whole it works. It's probably just as well that he didn't try to make a monument out of it, though.