Pretty nice game, needs some variance in enemies and their attacks though. I don't really like the random spray patterns of the shots. There should also be a visual indicator when your helmet breaks.
I think it would be better if you could shoot up/down the same way as left/right, simply by flying in that direction and pressing Z. Having to use X to aim felt a bit awkward.
Compared to your screenshots, I'm missing what I assume are health bars above the numbers (Linux version, the font also looks different so if you're using text rendering for the bars that might be why).