Its looking good. I like the extensive use of transparent bricks and plates.
Some hopefully constructive suggestions:
1. Get some dark grey or black 2x2 tiles with which to make a street grid.
2. You have white, light grey, and black buildings. An occasional tan, brown, or even red building would add variety.
3. Check out
www.bricklink.com
4. If you do get a larger baseplate, you can also put some low-rise buildings on the periphery to create a balanced skyline profile.
Question: does it have a scale? Some buildings use plates and others use bricks for stories (of course some real buildings trick the eye - for example the 40+ story Comerica Tower in Detroit looks like a 20 story building).
Keep on building. I think a city on 4 15x15 baseplates in that scale would look pretty spectacular.
-Jim