I love the atmosphere of the render, only a couple of things I'd've changed:
1. break up the snow line, it's a straight edge, put a bit of fractal breakup on
2. Shrink the trees - this scene has the look of something epic to it, and massive, and the trees are really too big for it, also put in more to compensate for the reduced size, but make sure to put a fractal into the density of the population, and maybe some tonal variations too.
3. Clouds are great, but the atmosphere could do with some more samples, that's what's causing that grainy look to it.
As far as I can see the image is perfect other than that, great work.