Impressively, I think it succeeded no matter which of its many genres' rules you measured it by. Which, I would say, include at least Fantasy, SF, Horror, Alternate History, and Postmodern Character Study. You'd think those would conflict, and to some extent they do, but Gregory leverages that conflict to make a more interesting and exciting story. Several times he uses a literary trick that reminds me of the Zen koan "First there is a mountain, then there is no mountain, then there is"; something which genre expectations lead you to expect to be one thing turns out to actually be something else (often humorously) -- but then turns out to fulfill your original expectations after all, but in a way that you didn't expect.
One aspect which I haven't yet mentioned is the degree of pop culture reference and nostalgia. It would be difficult to film this story honestly without paying tons of money in trademarks. Comic book fans in particular will get extra layers of satisfaction from this story.
It's not perfect. I thought he overplayed his hand in a few aspects, and underplayed it in others (no details; spoilers). Still, this was a *very* impressive debut, and I eagerly await his next work. Very Highly Recommended.
For more info on the author and his work, visit http://darylgregory.com/