Some thoughts:
1) Lens flare... baaaaad
2) Some opacity could be added to the windows to enrich the view
3) Search the web for more fre libraries or better yet buy some cheap...
You can start off here:
Got3d Free Textures - Free Tree Textures
Just some PS work and a little masking. For free.
4) The motion blur on the cars is too similar.. use some more variation.
5) The scene could use a warmer tint in some places.
6) Use some falloff or fresnel on the reflection - now it looks like its just a colour in the reflection slot.
7) The neighbouring buildings distract from the main focus of the image which are undoubtfully the two towers. Make them less saturated so that they dont steal attention like they do now. They also should be a little dimmer as they are sitting further back. That will give the image a more sense of depth.
Modeling looks fine.
Cheers : )