Nice idea, needs a lot of ironing out and a bit more of a strategic element. Unbalanced, also. It would be great to have special units/generals, skills, etc.
I love the music in the game, it's old and minimalist, lovely. I give it 4/5, since it's not really an original idea and it could definately use checkpoints.
Yeah, Kongregate challenge is pretty easy, you just need a Dual Machine Gun. I used that, 2 of those turrets for the damage buff and 1 Lightning Gun maxed out for damage.
Excellent game. Only moderately challenging and quick, though. Otherwise, incredible graphics and quite an impressive gameplay. I believe it constitutes a full 5/5.