I got 55 points. Still I'm not sure what's the difference between the light gray and white clouds. They basically seem the same.
The citizens are very slow so you have to wait quite long without being able to do anything and it takes really long for the clouds to take anyone out. Maybe it would be better if there were more citizens but with less health? Also maybe you could make it so the citizens run away faster the closer the cloud is so then you could get some more strategy involved?
It's a bummer that there isn't any apocalyptic music, because that would be cool.
Other than that I like the idea, and the graphics.