Couple things... first, I am not really partial to the textures you used... The background texture is not horrible, but I think you could find something better OR add a masked cloud layer set to overlay to give it some variation. The floor texture on the other hand is horrible. I would suggest downloading genetica view (free) and rendering some textures at the appropriate size to get something nice....

As for the torch light, it appears you are doing that freehand and it kind of shows. My suggestion here would be to set the GIMP grid to the same size as your map grid. Then turn on snap to grid. Use the ellipse selection tool and turn on the selection feature to ADD selections together. Once you have all of the torches selected, go to Selection->Save to Channel (menu item). Create a new layer and give it your torch color (some yellow shade and set it down to perhaps 50% opacity on that layer. Add layer mask to that layer and point it to the channel you just saved. Then click on the layer mask itself in the layers dialog and run a gaussian blur on the layer mask (play with the size, but 20 px might be a good starting point. This will get you a nice fade out effect glow.