I used to think The Rats in the Walls was but I have recently been re-reading his material and I find The Colour Out of Space to be one of his most intriguing ideas, with a lot of interesting elements happening within it: like more people than just the narrator involved, the effects that the event has had on an entire area, and the potential for overwhelming destruction.

Love this story. Actually did a reading of it for a podcast (episode never came out), and it's really difficult to read it out loud due to the alliteration throughout.