wow...
I died on day 43 and i had 174 gunmen, because a fucking invincible mech spawned and i couldn't kill it. I don't think i've ever hated a game more in my entire life. As for the people saying the minigun wont work, that's because you're retarded. You have to hold down the mouse to use it.
Some things to improve on would possibly be the enemies' movement paths. If you felt like it you could make them run vertically and horizontally, and not just in a straight line.
And no i won't be surprised if someone flags this comment for flaming, even though i added constructive criticism.