Hey, now that looks great! I like the shelf a lot. I like the newer doors as well. The drop shadow pulls them up from the floor nicely. I think the map as-is looks pretty done actually.

I've got a few comments about the map design though - not things I think you should worry about changing now, but rather things to think about next time. The floor looks like rough dirt or stone, but the walls are cleanly dressed walls. That seems a little inconsistent. Secondly, as this is for VTT use I'd suggest doing the wall shadows differently. Many VTTs are now implementing light sources, so it looks a little strange having a directional drop shadow. Also, you then require every object placed within the map to have the same directional drop shadow. This is fine (if a little fiddly) if the objects never move - but say your players spi a table round. Then the drop shadow will be going the wrong way. It's best to use no drop shadow - or a universal outer glow - to make it versatile. However I am being a hypocrit as all my outdoor maps have NW lighting and directional shadows - because it just looks prettier. I'm happy to take the slight drop i usability for the prettiness factor.

The only other thing I'd suggest would be to grunge up the floor a bit. Get hold of some grunge brushes (a search on deviantArt for Grunge will turn up many), import them into your brushes folder in Gimp - should be in C:\Documents and Settings\<userName>\.gimp-2.4\brushes and refresh the brush palette in gimp. Now create a new layer, set the mode to burn and pick a very light pastel colour - pastel red is great for blood. Pick a grunge brush you like the look of and paint a few marks on the floor. Play about until you find something you like. It's a kobold lair after all - the floor should be a little manky.