Ildu's point about the camera is good.
You might also want to consider playing with geometry more. A few interesting shaped buildings, arches, hand rails, etc. would go a long way. With a flat-shaded style, you won't be able to use lighting to spice things up and build atmosphere, so some neat base shapes and scenery will fill that void nicely.
I have a tendency to make boxy buildings myself. I swear, 90% of the rooms I draw are rectangular solids with holes drilled in them for doors and windows.
You might also want to consider playing with geometry more. A few interesting shaped buildings, arches, hand rails, etc. would go a long way. With a flat-shaded style, you won't be able to use lighting to spice things up and build atmosphere, so some neat base shapes and scenery will fill that void nicely.
I have a tendency to make boxy buildings myself. I swear, 90% of the rooms I draw are rectangular solids with holes drilled in them for doors and windows.