Soo.. all enemies are "grey colored" but definitly visible so this doesn't really match the theme.. I really liked the music and the background image :) 

Clunky and slow. The ducking animation should have stayed down if the key was pressed and kicking the enemies who came from behind me was kind of silly. I thought the look was good, but the invisible enemies weren't utilized well, because they weren't really invisible and it didn't fit the game in my opinion. On the positive I think the logo you've made is very eye-catching. Sorry for being so harsh. I think the game would really improve with some minor adjustments.