Keeping backstory a mystery

Over the weekend I became obsessed with the TV series Arrow (seriously, I watched the entire season over the weekend), and the one thing I loved about the show, besides plenty of eye candy in Oliver Queen himself, was the way they unfolded the backstory. Instead of unloading the entire five years worth of backstory about what happened to Oliver while stranded on a deserted island onto the viewer, the screenwriters only let out little bits and pieces as needed.

Watching this show got me thinking about how to dish out the backstory in my stories. I, for one, don't like being given all the information outright as I like some mystery to still remain or the story I'm reading becomes boring. Too much information too soon can bore the reader and make them lose interest in the story, but then there's the other spectrum (which I am often guilty of, especially in my first drafts).

I have been told by critique partners that I don't give enough of my backstory because I don't like to give away some elements that I want to be kept a mystery. Yeah, which can be a mistake and confuse the hell out of the reader (especially when my main character says "at least I didn't kill him" out of the blue without any other mention of this guy she 'didn't kill'... I'm working on that).

Getting the balance between too much backstory and not enough is a tricky business, but when it all comes together it helps to make the story interesting and capture the readers interest.

So what about you? Do you struggle with when and how much backstory to put into your story? For readers, do you like reading a lot of backstory or do you like finding out little snippets here and there?