Two words my dear fellow: SPOT ON!
Really really colorful and VIBRANT as it is visible from miles and miles.
Almost there:
Yeah, fog color needs some serious work. Play with different tinting values and density to see what fits best.
Now, aside form the obvious, which I think you already know(if you don't, then my bad, it happens), this needs some recognizable ground vegetation.
I know that it is supposed to be up there in the mountains but even up there, scarce foliage and some lichens can be found reeking a living.
Not to mention the lack of water features, like waves and colors.
That 'fountain' just doesn't make sense right now. There's no natural way around it, no grass, shrubs, smaller trees. The scale is off as well. Perspective is thrown together when you first look at it.
Crystals seem stacked together with no discernible formations and are definitely over-sized like hell. I'd understand if this were a white dwarf(diamond ball in the sky) but this....
Then there's the end of the world. Like, why in the world's sake would you just leave it open instead of adding background details like hills/mountains, forests, mist. Anything really that makes your terrain seem endless not looking like the edge of the world is just beyond the horizon.
As for the vanilla units, just a big NO. If you start with HQ models, be consistent and keep with HQ resources until the very end(that or put the low res ones far from the camera's scope).
Thanks ! 
