Great work in this thread Stuamn. Also nice to see a fellow Gimp user in action. I love the last map to for KoSF. Just a suggestion regarding shadows. I think you have used Gimp's drop shadow function. The only problem with this is that it tends to give the impression that the foreground items (walls and pillars in this case) are flat items floating above the surface rather than solid items rooted to it. As an alternative you may want to consider creating a duplicate of your black foreground layer and shifting it slightly and applying a gaussian blur. Then place the blurred layer below the foreground one. Another shadow effect that I really enjoy is to use the motion blur function. This, to my mind, looks the most realsitic for slightly diffuse shadows.
Keep up the great work.