Thanks for the feedback. The fullscreen thing is a deliberate decision. I didn't want the game going fullscreen because that would either stretch out sprites or widen the player area and visibility. So if you select fullscreen it shrinks back to a window of the resolution that was chosen.
The half circle powerups let you speed up the ship using the toggle speed button. It would help to have some kind of "How to Play" section in game.
Auto fire never occurred to me but that's a pretty good idea. The player would lose precision but it's something they could use if they wanted as long as the auto fire rate wasn't inhumanly fast or something.
Thinking about getting the bullets to pulse a wider range of colors and faster to make them really stand out better.
Having warnings to indicate when things are coming from different parts of the screen is an interesting idea. It could make the game more playable and also open up some different encounter design.
Appreciate the response.