Earth-Sim takes a wonderful concept, molds it into an enchanting story, and then obliterates it with soap-opera antics and mind-boggling plot departures.
I was enthralled by the description of our entire universe as nothing more than a classroom project, especially one overseen by two accident-prone undergrads. The plagues of Egypt, the disappearance of Atlantis, and crop circle formations are all academically attributed to such mishaps, while various theological texts are framed in the context of controlled experiments and lab notes. Visions of holy beings are manifested as nothing more than environmental tweaking, while the blame for Earth's greatest deluge is placed solely upon the shoulders of a student's clumsy sibling.
This framework made for a clever tale and a fun read, right up to the point where the story collapses beneath its own whimsical weight. The undergrads are approached by another world-building team, who asks them to babysit their newly-orphaned Kryptonian. Earth's history is suddenly populated by comic-book aliens and mutants. Shortly thereafter, our heroine is dramatically revealed to be a galactic empress, tormented by the loss of a socially tainted step-brother--a deus ex machina that generates the Bible, an invasion by waves of Terminator-like beings, and (blissfully) the end of an increasingly chaotic narrative.
A compelling society is hinted at throughout the book, but never adequately explained; advanced AIs are squandered on plot-hole patching and comic relief; and the characters--compelling though they are in the beginning--end up as fairy-tale caricatures of themselves. I rode it all the way down, but I was sad to see such an intriguing idea crash and burn.