You've either got to find a way to make your continuing characters insteresting without making them maudlin or overwrought, or you've got to put more emphasis on the suspects.
The scariest movie I have ever seen, and my favorite horror film is, 'The Exorcist.' It is a must-see horror/thriller classic. I watch it every couple of years.
This would only come if you have a revolutionary change in technology like the jet brought about.