Maybe Steven Moffat desensitized me, but it's hard for me to get excited about monsters you can't see. It feels a bit like a cheap trick to create "psychological terror" with little effort.
But the book in general was underwhelming. The housemates were flat - I can pretty much assign a Ninja Turtle to each one (except for Jules, because there was no "animal-lover" ninja turtle, and Olympia, who's "Pregnant Turtle") and that would be sufficient to describe their character... Even the protagonist herself doesn't really have much of a personality. Not to mention the kids, who are little more than a plot device.
The story could have been a lot more than it is at the hands of a more skilled author. Even the ending, which is probably the best part of the book, suffers from this jumbling feeling, where more stuff is just piled on top even though it doesn't really add anything, and just slows down the pace. What was the point of the whole blinded people bit? Did it really contribute anything? Were we supposed to think for 20 seconds that she reached a hellish place? It never went anywhere, it got resolved in half a page, and then the book ended. What was that for?

It's not that it's a bad book, but it's just not one of the best out there recently.