Eskandare, great maps.

The Imperial Prison and Command Centre maps are very well done. Very clear but also interesting. The colour scheme works nicely overall and its great to see a map of this type that isn't a riot of clashing colours. Great lighting too in the room with the metal floor. The only criticism I'll make is that the red symbol on top of the olive-green bins in the centre are a bit too red - it looks out of place with the rest of the map. This red needs to be toned down. Also the yellow danger-tape lines along the west of the map come out a rather sickly shade due to the underlying blue - perhaps add a good bit more orange to that shade, something closer to directly opposite the colour wheel (R100% G75% B0%) rather than at a quarter of the way across like you have now (R85% G100% B0%). Rather than reducing the opacity of the yellow danger lines (and indeed the red symbols on the bins) you can make them look old and flaked-off by adding a layer-mask filled with a plasma or cloud layer. I agree with Kestrel that the blood is a bit limp too - you need to make it much darker brown in the middle, only that colour at the very edge.

I like your swamp maps. I don't find the grid too bright or distracting - I think you did that just right. Great use of Neyjour's mushrooms - they look great here. The only thing that does not work for me on these two maps is the shorelines of each of the islands and river-bank. I can see what you are doing with your sandy transition, but I don't think it looks good, and also swamps don't have much sand. If I were you I would get rid of the sand and make this a simple step, with shading to indicate the two levels. It will give the maps a more 3D feel and clear up the colours a little.

Also, these maps you say the original adventure gave you - is this a commercial product? I ask because I recognise elements created by a member of these forums (and for sale elsewhere) that are clearly not the work of the black & white map artist above.

Without access to Photoshop I'm stuck with using GIMP, Inkscape and Paint.
This is not quite as terrible as you imply - and you did a great job anyway. What do you use Paint for that Gimp and Inkscape cannot do?