I'm not a fan of endless mystery in storytelling - I like to know where the mythology's going; I like to get there in an exciting, fast-paced way - enough that there's a really clear, aggressive direction to where it's going, to pay off mystery and reward the audiences loyalty.
People pitch me the crazy mystery mind-blowing thing all the time. My response is, 'Great, but how do the characters feel about it, and how do we reveal new facets and new dimensions of who they are?'
Religion and gods and beliefs - for me, it all comes down to your brother. And your brother might be the brother in your family, or it might be the guy next to you in the foxhole - it's about human connections.
Every so often, you want to map out your plot mythology but never so specifically that you can't let a story surprise you. You want to allow the type of action of the writer's room so that you have the ability to take a left turn.