Hi mboncher,
This is just my 2 cents please feel free to disregard if you like. In my opinion the problem with the composition is the perspective is all over the place. I would go back to the default camera view straighten the castle up and line all the horizontal building edges up with your wireframe grid. Lower the depth of field a bit. It's stretching the terrain texture in the foreground. If you want to show distance I would lower the horizon line a bit and increase the atmosphere some more rather than rely on depth of field to give you that distant feeling. Try fiddling with the grass texture on the nearest terrain to the viewer. Maybe instead of parametric try object space. Leave the distant terrains parametric. This will also give you more of a distant feel.

The biggest problem I think is you haven't well defined a main focus. Connie is absolutely correct when she suggested to bring the cat closer, and enlarge it so that it becomes the focus and the main subject. The terrain should be the secondary focus. turn that castle out more rather than in towards the center of the composition. That will do a great deal to fix your perspective problems. Maybe even bring the whole castle closer and just show a part of the castle that the cat is sitting on. Once all that is done, then bank the camera if you want. The problem is it needs to all be lined up right perspectively before you can bank the camera. Or it all just looks skewed.

Try different textures on various areas of the castle. The lower wall would be slightly different than the walls of the roofed building on the top. That's certainly up to your creativity.

These are just my observations anyway.
Good luck.