Not bad; could be better.
Suggestions: it's painful to have the workers follow the mouse ALL the time; you should be able to click on the gold and then leave them there until it's mined out.
In addition to being away from the shelter, the port pad should ALSO be away from the top edge (or at least the top left corner, in my experience), otherwise the soldier just shoots off the top of the screen and/or gets touched by some invisible zombie. Regardless, he should ALWAYS shoot at the zombies attacking the shelter OR be able to be controlled by the user (click-to-target, perhaps).
A pause button would be nice.
The score really shouldn't start counting until the zombies come.
I guess that's it for my comments. Good luck!