It seems to me that we spend most of our time considering the hero.
But what about the ANTAGONIST?
"A hero is only as strong as the antagonist."
~ Janette Rallison
I don't know about you, but I think that's true. The villain tests the heroes abilities and worthiness. Overcoming the villain is usually the main goal of the story. If that task isn't a HUGE challenge... if the antagonist isn't a scary S.O.B, then our heroes status doesn't grow or show like we want AND need it too.
That being said, the villain/shadow/antagonist doesn't necessarily have to be a person. It depends on your book or your genre, but the person/object/event that the hero fights against needs to be great enough to show the true strength of your character as they fight to overcome it.
One thing I think is important to remember is that the villain needs a story too. (This mostly relates to a "person" villain.) But they need to have goals, and motivation too. Give them a little back story so we know their motives and why they are so evil, or why they create such a conflict with the hero.
What do you think? Do you think the antagonist needs this kind of attention in a story? Do you like to use a person, object or event as the main conflict of your story?