One of my biggest pet peeves when reading novels is when the narrator doesn't reveal everything they know, espcially if it's written in first person. Don't get me wrong, I love twists and having to guess endings, but when a crucial piece of information is withheld from the reader, then that's one of the main things that makes it hard to continue reading.
I have read several where the character turns out to be something else (one wasn't even human), but they were portrayed as ignorant for half the story. So, how should one choose what to divulge? I like to create detailed character sheets about my character and decide what the reader needs to know. If the lifestyle of the character is important, then that character should at least mention it... it's not a twist if the reader comes to not trust the character.
So, how do you choose what information to reveal in your story? What is your biggest annoyance with novels? What makes you stop reading?