Pointless difficulty
The fact that you can't see anything outside of the small circle that you shoot through makes the game hard, true, but I disliked it for 2 reasons, 1)There's no way I could move the view to every part of the screen before getting shot but the unseen enemy, and 2)There wasn't any real reason for it to be there. Maybe it'd be better if you just had a dark fader over the rest of the screen so it was difficult to make out, but you could still recognise movement. Just an idea. Good job for the most part.