I'm going to have to agree with a lot of people on the comments, the twitching is not realistic at all and makes it nearly impossible to hit anything, especially with the x4 scope. The penalties and lack of room for error on how you spend money is devastating, making you want to restart the game several times just to afford equipment that you cannot get far without. I also had trouble with getting an error message when I either didn't have enough money to buy something, or already had it - even when this wasn't true - that would refuse to go away no matter how many buttons I mashed. If these things were to be fixed, I think the game would be much better, I enjoy this type of game and there was clearly time and effort spent on it.
I like the general idea, but I seemed to have a couple issues. One: I seemed to have no available survivors when I clearly had around 10. Two: I had zombies walk right into the range of a tower and it would not fire. It had ammo and about 5 people in it. Other than that it's okay.
I really really enjoy this, I'm not sure why. Once you figure out what does what, you can make some very interesting designs. It would be cool to see more done with it, such as descriptions of what each tool does, new tools, ect.
I'm impressed that you tried using the turning the wheel sort of steering instead of "this arrow goes this way" kinda thing. Thought like other people have said, it's very very sensitive, that part could use some work.
Problem with the controls that I usually have with mouse following controls: the game requires I fly close to the edge of the game window, but once I leave that window the direction its moving towards stays where my cursor was last, making it difficult to maneuver at the edge.