First, let me say that I think the "The Mountain" scene by Dynamite is spectacular. Pretty much flawless in its execution and color design (really, just superb usage of that purple "after the machine turns off" tileset with a great looking vivid sunset background), although I think the trees don't really mesh quite as well. That's the kind of usage of an old tileset that I really feel like I should've come up with, and am sad I didn't.
Second, I downloaded this level specifically for HeadGrinder's section, and here's a few comments for him, as a kind of reciprocity for what he did for me:
The black lines around most of the objects in the tileset are rather jarring (maybe make them less noticeable?) As are the textures in the stones (the light-colored ones, especially, though the purple ones might could use a bit of work, too, in order to give them the professional looking texture of Nifflas' tiles). And while I found the stones to be quite appealing when big and rounded, the white ones again look a bit odd to me when squeezed into tight, angular forms. That might be personal preference. Also, of course, the stones are not easy to traverse in a game built for very geometric ground formations. Completely understandable, of course; a design decision one has to make, likely. I'm also wondering if a differently-colored and or shaded background might look better against the purple stones.
Other than that, though, I say very nice effort which pays off pretty darn well. I think the fuzzy, cloud-like, largely-border-less organic formations (with the flowers on top) are very cool and do look great. As a main contrasting element to the purple stones, they work fantastically. They might look greater in conjunction with some slightly altered purple tiles, as I said.
P.S. I know the bulk of the criticism reflects badly, but don't let that make you think I don't like the tileset.