The principe of the game is good. It is good idea to search every your bullet. The game becomes harder. Maybe change something about movement of ennemies. I think they move fastly, reduce their velocity can be better for some ennemies. You can also reduce the size of detection when they begin to chase you because when they are a lot of ennemies on the screenn it becomes difficult very quicky (too quickly ?). 

But great work :) ! 

That  was a pretty cool concept. Loved having to make my shots count!