Found a glitch: If you're reloading a gun and you switch to another one, the ammo number dissapears and you usually can't fire. Scrolling the mouse wheel didn't work. I tried pressing "e" and it changed and started working properly again though.
Whew, that was tough, but finally beat all the levels. I thought the last few had good level designs, but if you died it was waaaay too frustrating. 5/5 regardless though.
 "Achievement Unlocked"){kind=icon}
 "Eternal Red"){kind=icon}
 "Portal: The Flash Version"){kind=icon}
 "Dark Cut 3"){kind=icon}