Characters hook an audience. Readers remember Sherlock Holmes and James Bond even if they forget the plot points or dramatic details.
What is character? Writing + acting = character.
The most memorable characters from classic films and TV shows are created by chemistry. The chemistry that occurs when the right actor meets the right part. This is why it's been said that 90% of directing is casting.
What has this to do with scripting a horror film?
When I first saw Dawn of the Dead it blew me away. I was in my teens and had never before seen such gore. But after thirty years of horror, I'm bored by gore. Actors in bad makeup eating bloody intestines put me to sleep.
I think this is why so many zombie comedies are being shot. Hardcore horror fans are jaded. At a certain point, gore alone looks silly or sordid, rather than scary or shocking. Filmmakers can try to "push the gore envelop," but I'm not sure there's anywhere left to go.
How then to engage audiences for your latest horror film? Character.
Horror films have been compared to rollercoasters. To which I'll add: characters are the car. A great character engages an audience. Audiences sympathize and empathize with the character, getting into the character's skin so they can "suspend disbelief" and enter the character's world, being shocked and frightened by whatever shocks and frightens the character.
Effective characters take audiences for a ride on the coaster. Ineffective characters leave audiences standing on the ground, outside the story and looking up at the coaster. They see it twisting and turning, but they're not on board experiencing the thrill of the ride.
How to create an effective character, one who engages an audience? Audiences should care about the character, but that is not to say the character must be likeable.
For more about creating an effective horror story, especially on film or video, see Horror Film Aesthetics: Creating the Visual Language of Fear. This blog represents a continuing discussion of my views on horror, picking up from where the book left off.