Greyish tones are fine for dull and rainy days, but with a nice blue sky you could expect more contrast.
Couldn't agree more. If you load a screenshot from the game into Photoshop and take a look at the levels, you can see by the graph you don't have a full range of tones. The graph should start low in the left corner, build, then fall-off to low again.
Apart from that it's looking very impressive.