I like the composition, the linear perspective is pretty good too.
Things to improve would be research atmospheric perspective. Its also sometimes called aerial perspecive. Basically the principle is the further from the camera all colours take on the colour of the atmosphere (in general they become desaturated). At the same time, contrast reduces. This means the blackest blacks in the image are close to the camera. You just need to make sure this rule is applied consistantly throughout the painting.
Also, shadowing and colour: a few areas of the image, like the castle look like the burn tool has been used to add shadow. This has given the building a bit of an orange/red look which is slightly unnatural. When I add shadow I usually paint on a multiply layer.