Excellent!
This is a great game, but as many other's before me have stated a few upgrades would be nice.
1: Maybe make the red cursor go green when hovering over a enemy?
2: Music. :)
3: What I would love to see is being able to walk out the shack and attack on foot, they would greatly improve this.
4: Make the prices lower, they jump from 100 to 500, altough it is easy to get cach, but you need a early defense to build up. (Those "jason" guys are hard!) :)
5: I fell that this could almost be a flash "Resident Evil" is you could move out and about, but otherwise than mine and other people's suggestions, this game is great, I really love it and it kept me entertained, well done. ^_^
And keep up the good work on DA!