I think the ground texture looks wierd because it is not the right scale. Can you scale down the texture in GIMP? Looking at that texture I would expect the buildings to be much bigger.
The river looks for like fake fur, than water to me .

You have a lot of space to fill and getting that all to flow and balance without detracting from the town can be quite a challenge. If you have a clear idea of how you are going to do the landscape and how it will compliment the city, thats great. ( Excuse me for butting in early) If not, ask yourself the question: how is all that space going to compliment and draw the viewers eye to the town? As the town is the main focus of the map.

In your poor area the buildings are very hap-hazzard and look like they have been randomly scattered. I imagine even in a slum, people put a bit more thought into where they place their structures. I would also imagine that in poorer areas buildings would be built up against existing structures to save on costs.

I hope that is helpful.

AP