A game based around the Cthulhu Mythos, except that, instead of following one character's story, you'd have multiple chapters to go through. I know it sounds a lot like Eternal Darkness, but it would be an FPS like Dark Corners of the Earth. The stories would be such things as:

-Exterminating Herbert West's zombie horde.

-Roaming through the mountains in Vermont, having an occasional encounter with the Mi-Go.

-Eradicating cultists and their leaders.

The horror elements would be more psychological, such as background noise, or oh-shit-they're-following-me moments.