This science fantasy is very different from John Scalzi's other work. It starts out dark and gets darker as it goes along. Some of his readers might be so surprised that they won't like the book (it's not a novel; it's a novella). Others will love the new direction and want to see more. You'll have to read it to see which camp you fall into.
As for me, I enjoyed it, but my pleasure was marred by the kinds of things that don't bother anybody other than old English teachers. Things like the use of aide as a verb, or a sentence that begins, "Whomever he was, . . ." Or the misuse of lay when lie would be correct. There are a few other little things like that. Maybe Subterranean needs a better proofreader, but I make so many errors myself that I really shouldn't complain. But I will, just a little.