"The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst of black seas of the infinity, and it was not meant that we should voyage far." -- HP Lovecraft
This quote pretty much sums up cosmic horror as a subgenre. It lies along the edges of science fiction and horror, where awe and wonder become terror and dread, to the point that it can unhinge one's reason. Humanity has long seen itself as the apple of the Creator's eye, the apex of Creation -- but as we reach out into the larger universe, we discover that we have just been a big fish in a very small pond, but are in fact a minnow in an ocean full of vast and incomprehensible beings, to whom we are as insignificant as a colony of ants is to us. Even without malice, they can do us terrible harm.
This bundle is by no means restricted to direct pastiches of Lovecraft's works. They don't need to mention Cthulhu or Yog Sothoth or any of the other entities vast and deep which make their way through his imagined universe. But books in this bundle should evoke that sense of dread, of deep space and deep time as dread-inducing, defying logic and reason. Artifacts of impossible antiquity, books of knowledge too dangerous to study, and above all, the sense that the universe is not just stranger than we know, but stranger than our human brains are equipped to comprehend.
If your book has a feel similar to the Alien/Predator franchise, or John Carpenter's *The Thing* (or John W. Campbell's "Who Goes There?"), you're probably in the right ballpark too.
If your works deal primarily with the traditional monsters (vampires, zombies, werewolves, etc) or with the evil that human beings do to one another (Psycho, Saw, etc.), this bundle is probably not going to be reaching your audience, and you would probably be better setting up your own group promotion.