It really nails the theme of the jam. And it's fun to boot!
My only complaint would be on the graphis and UI. It's hard to parse at a glance. The shield's as a small text in the bottom right, is not very helpful. Especially if it's not displayed at all half of the time. Also, what is the Thrust there for? And, the background stars are the same color as enemy bullets which makes them hard to distinguish. Keep in mind these are nitpicks though. The core is great!