looks really cool, but the first level is quite hard. I like how you NEED the variation in the towers. 3/5. Would like to see a gradual change of difficulty(the ability to get past level one :P) and maybe tanks instead of bullet resistant people!
gotta say that the machine guns are very high powered, and that there isn't much, if anything, that can get past a good placement. Maybe they should be worth more, or have less damage! Very fun though, and it looks really good, maybe add some more visuals, or change the gamma for night and day...