This is not mainly a book about The Troubles; nor about religion or politics, though it is about all of those. It's a book, above all, about gossip and rumour and silence, and the harm that those can do to a person, to a society.
The unique approach — no-one is named, almost no proper names appear — I found quite endearing. And far from obfuscating things, it many ways it makes the story easier to follow. Instead of have to remember whether Mary, Margaret or Roisin is the oldest sister, it's “first sister.” “Oldest friend;” “maybe-boyfriend.” Honestly, all books should be like this. Relationships are important, after all.
Though you can also see it as a sly reference to the common complaint about living in small communities, that you're always someone's daughter, someone's brother — never yourself.
Anyway, Booker Prize winner, and all. Dead good.