The writing wasn't bad. The plot was pretty good. And it was refreshing to read a stand-alone book. (Yay!) And if you could set aside your incredulity of the concept that there are people out there who have zero capability to affect the world and that they can actually become invisible by their lack of importance, then you'll enjoy this book.
The one thing that bugged me was that one of the main characters, Claire, was pretty well-adjusted after a life of being ignored. And what I REALLY don't understand is how she survived infant- and childhood. There has to be someone to take care of you - if you were a Nobody, no one would care and you would die.
But I tried to ignore that, too, and focused on the story.
Interesting concept, and well (as could be) done.