Fun game, but some suggestions:
1) Make it so that the items to click have a mask, so you don't have to click on the letters.
2) Make the shooting button something other than Shift because hitting it five times in a row prompts for Sticky Keys (even though it can be turned off, it'd still probably be better to make it 0 on the keypad or something)
It would be great to select from multiple chars that have different pros/cons like: one has great speed, but slow rate of fire; the other has slow speed, but a much faster rate of fire. Know what I mean?
Pretty fun though.