The menu screen looks great.
The atmosphere is really good. It's not a horror game, but it still made me feel a little uneasy.
I'm not sure if it's intentional, but since the shots don't come from the center of the character, I had to aim slightly above enemies at long range. It made the game a bit more challenging, especially when dealing with the mites, since they have smaller hitboxes.
I also would have liked to see a "You scored X points" screen after dying.
Simple, but good. :)