Pretty cool game! Some of my considerations:
- Boss design is on point. I like that they use the abilities they're about to give you. The second boss crawling on the walls was so satisfying. Certainly one of the greatest aspects of the game.
- The way the ship turns makes it a bit difficult to aim on enemies.
- I agree with the afterburner thing (a faster recharge would be so nice)
It was very fun to play and I had a great experience overall, lots of puzzles here and there.
Oh, and about saving, maybe an idea would be to have a specific place where you dock your ship to save, because you'd have to get out of your way to go there, which is an indicator that you really want to save. That way no buttons would be needed, I think.