Well.. I have to start with commenting the square form of the city. Well, I don't like it to be, sorry. But other than that I think it looks great!
It's very thick. And I don't see any gates? Maybe some towers spread among it will make it look more like a defence than a pile of rock.
I would add some depth to it, I like the colours that you have used, but I don't look too realistic around the "coastlines". Maybe putting a drop shadow on the land? Or the opposite..
Maybe if you picked a scattering brush around the edges it would look more like trees? And putting some single ones in the city, around the river and along the edges of the map.