Created and composited in blender 2.59
I feel the horizon is a bit low and the sky has bad resolution, but the city looks convincing, well done!
Overall not bad but the repetition of 4-sided box shapes and lighted window textures is not very convincing. Gather some refs and see how much variation there is in architecture, window shapes, and what proportion of windows are lit at night. External lighted signs and some indication of street-level lighting (it would filter up to this level somewhat) would also be helpful.