The atmosphere really is nice .

Here's a piece of advice about the rest:
* Get rid of the tent and structure-top on the bottom left. Try to create some dead trees instead.
* The second building from the left needs better painting - It's colors are pretty ridiculous (to much, to bright green and yellow).
* Add some low-density dirty fog.
* Add a polluted cloud on top and maybe some toxic waste in the water.
*Improve the shape of the bridge:
- Instead of /|---|\ try /-|---|-\.
- Where it breaks try and put some big rocks on the edges of the river, and show how the water is flowing around them.

Hope this helps,
Benny