Constructive criticism after a long waste of time.
I just got to day 21, and I am seriously aching for that time back. It's about a half hour of my life which I'll never see again.
I played it on normal, but I was expecting some sort of increase in difficulty as the game progressed, regardless of where I began. After I got the laser cannon thing (which was 3rd or 4th day) it was GG for the aliens.
You should either have the difficulty of the aliens increase as the game elongates, or make it MUCH, MUCh more difficult to acquire money. As it stands, I'm pretty sure that if you plummit all of your funds into the shield, you can go watch some seinfeld and not have to worry about anything touching the base.
I don't think that should happen.
The game really isn't that thought out and it's nothing different from any other similar game.