Well, I ALMOST beat the game.
I ran into some frame-rate issues, but I think that's because of my current hardware. As is, the game was a lot of fun. I thought the music and environments kept me totally immersed. Being a gun threw me off though, I was not expecting that! Something else unexpected I DID enjoy a lot was the gun's kickback. It felt really responsive and switching between weapons was seamless.
MAYBE toning down the difficulty would help. I can't count how many times, I was fighting off enemies like a hungry dog for the extra ammo and health.
Overall, magnificent work.