I'm pretty sure everyone can agree that almost every story needs a PROTAGONIST and an ANTAGONIST.
But when the Protagonist is an innocent goody-two shoes who shirks at the thought of killing anyone, and the Antagonist is some form of Pure Evil, things tend to fall a little flat.
Don't forget your shades of grey.
Every human beings has flaws and WILL make mistakes. They are also open to temptation by things that are wrong or evil. If you don't force your characters to ever face the darker side of themselves, they aren't real people.
There's a trend of anti-heroes showing up now, but alot of them are all the same. Badass, hot guys pretty much. Basically, they kill people or belong to some typically evil race (i.e Vampires), but it's cool because they've got a soft spot for the girl protagonist, or are 'misunderstood'.
How about a different sort of anti-hero? How about a babysitter that loses her cool and accidentally kills her friend's child? How about an orc that smashes people to pieces but would never abandon a fellow orc? Give me something new, something a more interesting shade of grey.