I would work on your perspective before anything else. See how you are looking up at somethings (like the castle on the left) but down at others (the tower on the right-- see how you can see the roof?)? That's not how "real" perspective works.
Although it's a tricky topic, there are a lot of resources out there. For example: http://www.elfwood.com/farp/perspective/perspctv.html
has a good overall take on the various perspective systems. I'm sure a search on youtube would also show some interesting results.
Hand in hand with the above comes a lack of depth. The front of this has a bunch of things all in a row, and in the distance we see some mountains. There's very little connecting those, and it feels like all the castles and towers in the front are all in one big plane. That can work as a stylistic decision but would be rare for realism.
Hope that helps!