God Game has enjoyed a high profile on my bookshelves in various homes since I first read it circa 1990, because it was a phenomenon.
Oddly, the impression I had from reading the blurb -- that it was going to be like a game of Populous only with named characters -- lasted more strongly than the actual content of the book once I'd read it.
The actual book uses a science fictional lighting-strike as the device to bring the narrator into a god-like (or God-like) relationship with the Fantasy-ish characters in a game, but there the science fiction and fantasy end.
The book is about the relationship between an author and the characters in his work who take on a life of their own, and how this might relate to a monotheistic God's relationship with His/Her free-willed creations. It's immensely, name-dropfully, erudite in the philosophical and literary spheres (esp. John Fowles for Mantissa and Flann O'Brien (sp?)) and probably just as sophisticated on Christian theology, though it keeps that more under a bushel. It reads affably, albeit with a rather self-indulgent authorial voice, plus interjections from the author that the narrator of this piece of fiction is another character, and not him himself. But with all the thought-provoking reflections and the possibilities that he science-fictionally set up for himself, the actual story he ultimately wrote was itself only so-so.
And the central importance of a Shakespearean fool, cast as a puckish nubile teenage girl often gambolling in a swimsuit, is just discomforting.