This debut novel actually did have some promise to it. The world was fantastically scary; that wonderfully scary cover is actually relevant to the plot of this book. So, I guess if you're looking for a good Halloween read, you should check this book out.
But in terms of actual character development, The Replacement was a complete dud. Mackie was just one big disconnect: all tell, no show. I never got a fix on his character... probably because he didn't seem to have one. And none of the other characters were any better. There's usually at least one in every book that I want to see more of, but not in this one. Had the book ended with everyone dying, I would have been completely unperturbed.