What Don't I Get about Unreliable Narrators?

I picked up an author I hadn't read for a while and was halfway through the book (a thriller with your everyday serial killer) when I realized the characters were holding out on me. That's the polite way of saying the author cheated.

When I am in a character's head (their point of view), I expect to know what they know. Not what their favorite uncle gave them for their last birthday, but anything that relates to the story. Sure, a character doesn't spell out what s/he will do in advance -- that would be dull. But to get three-quarters of the way through a book before you find out the killer's motive is totally different than presented? Not presented by a reporter or neighbor -- told by the killer. Argh!

Writers approach their craft in so many ways, but the so-called unreliable narrator makes no sense to me. I read Mary Stewart's The Ivy Tree when I was twelve or thirteen.

Every time my mom read a book I picked it up when she was done. In that story, a young woman shows up in a British town and spends the entire book denying she is someone who vanished years ago. At the end of the book, you find out she was in fact the long-gone woman. It was her point of view!

I told my mother I thought it was the dumbest book I'd ever read. Her response? "I meant to tell you not to bother." It was years before either of us trusted another Mary Stewart book.

Any comments from readers or writers about why they think this technique has become acceptable? Did it take hold with Gone Girl? I'm still furious about devoting time to that book. I like a mystery that's truly a puzzle to solve, not a 'surprise' ending because a character holds out on me.

I wish publishers would decide it's a genre, then I'd know in advance to avoid such books.What do you think? Have I turned into a fuddy duddy?
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To learn more about Elaine's writing, visit www.elaineorr.com.