Love it, coming along nicely man.
Just as a suggestion, if you haven't already tried; You may want to try adjusting the ambient light color in "Render Settings." It's a free change performance wise, and you might be pleasantly surprised by having the shadows and overall tint no longer gray scale. In the same area you can also add fog, if used subtly it can add some moodiness to your scenes as well.
Keep it up!