Nice one, Scott!
I like the use of the limited palette, it almost seems monochrome at first look but it has a lot of hidden subtleties which really work nicely.
Back in the late 90's I illustrated the "Beyond the Mountains of Madness' campaign for Chaosium, and I was asked to paint a similar scene. When I think of all the challenging illustration topics Lovecraft created, I think this one might be at the top. Trying to paint as realistically as Pickman is hard, trying to depict indescribable ever-changing horrors is hard too. But, trying to paint in an art style that we have never seen and likely would have taken decades or centuries to develop?
I think we have a winner, especially when given less than a day to do so.