Nice concept ! I also like the upgrade system. I think an 8-direction movement system would make more sense for the kind of gameplay you have

I really like the idea of the ship being able to block bullets and the core being the actual thing to protect. The physics of the core being chained to the ship add to the challenge. The roguelite elements are good and make it fun to play through until the end, the cards could use some more variety but that's fine.

Minor bug: bullets can hurt the core after you've completed a wave.