I have grumbled more than once in these pages about genres as something that comes between readers and books they might like: my argument is that genres are more useful for marketers and bookstore staff than readers (or writers).
It didn’t fit any categories, and thus would suffer the worst fate of all for a book project: bookstores wouldn’t know what section to put it in. There is no surer death-knell for a book project than that.
<update> further discussion of this idea is here.