Slaughter! I love it!

Graphics: excelent. mothing to improve, only give me some blood when bullets hit.
sound: great. let's hear some music and maybe alien attack sounds
gameplay: ready for this?
you need
-multiple guns. i love your system as it is, but you REALLY need to have more guns. maybe keep the ability of akimbo, but make it so that you can pick up guns for left and right hands. I want to see a mp7 and a double-handed gun, like a g36k.
-varied enemies. they shoot easily dodgable bullets. make something cooler.
-varried challenges. shooting enemies gets boring after a while, and you don't even need to kill them to advance.
-clips. the guns never run out of ammo! you need to reload if you unload too much on an enemy.

story: awesome. nothing to improve.
interface: maybe the right hand fires with right click, left click fires left? but its pretty good.

just work on the gameplay! you've got a great game going here!