Congrats on a great game.
Amazing. I can see this really going places.
I remember seeing a game like this a couple of months ago. In fact, I think it was the same maps, but there wasn't really any game play. It was just a simulator. You'd input how many police/civilians/zombies there were, and the map would play out and you'd see which side win.
I hope you were involved in that project, because otherwise this is partially stolen. I'm going to give you the benefit of the doubt though, because I assume you were involved, and if you were not, then you still deserve some credit for the extra effort you put forth to make this one a lot more interesting.
Now, in terms of the game. There are a couple of simple improvements that I would suggest.
1) Controls. Like a lot of people already said, make it easier to select your units. A drag selection tool, with the ability to select multiple groups at once, would help out a lot.
2) More maps. Obviously would help extend the life of the game.
3) Most importantly, add more dynamic elements to the events that are happening.
Add a couple of more things that you need to do before you get to the chopper. Retrieve parts for the chopper, find vital notes from scientist, rescue additional trapped cops to bolster your ranks.
Or, we could be given the ability to find other weapons or vehicles (although this would require lots of additional programming, that might be difficult). I'm thinking a jeep to drive you around to all of these extra objectives would be fun. :)
If you add extra elements, you could also randomize which scenarios play out, and where they are on the map. This will keep people playing your game for a long time to come.
Additionally, make us have to fight through more zombies to get to certain objectives. Both maps, I mostly just ran and easily escaped almost all confrontation. That might have been what you're going for, but what people liked most about this game are those small moments where you were becoming surrounded, and you didn't know if you could make it. However, once you get a feel for the game, almost every situation is easily out maneuvered.
Again, great game, and I hope to see another one from you in the future.