This was fun! I really liked this game, the machine gun, and the slow-motion on level completion was great too.
I think you have something fun here, and with a little more polish you'll have made a great game! I suggest you add more "juiciness" -- I'm not sure exactly how though haha. Maybe you can add some flashing lights along with the slow motion effect. Also, maybe you can add a split second pause on the frames when an enemy is killed.
In any case, great job. I had fun playing!