I've always thought of the uncanny valley in 3D spaces to happen most often when folks use digital photographs with virtually no editing or thought how they
fit into the 3D scene. One trick when making textures, is to make a texture
from hand and use it as a pallette/get your colors from it for other textures on the same level.


What is the differences between the two images in the first post?

I'm not sure the uncanny valley is the issue here as much as color theory.
First, both images show quality work; however, the myst image has a limited palette
range with warm colors vibrating off the cool waterfall colors. You want to control: contrast/limit palette, and use basic color theory to decide which colors to combine...to set the mood.

I think the first image/3Dscene is fine; however, it has more potential to evoke a mood with adjustments to the lighting. Ask yourself what mood you're trying to achieve-- what is happening in the game?

An easy change for the first world would be to replace the skybox with a different texture-- a sky with some elements of purple would be interesting-- a sci fi planetary nebula or some such. Why purple? Purple is green's compliment color, but that might not work for the mood...