The bubble graphic looks really nice. I think that the difficulty maybe didn't scale up enough as it never really became challenging (I finally let the enemies kill me after a few minutes). A score, maybe some bigger enemies that need prolonged contact with the shield, some variety here would have helped possibly. The code appears to work very efficiently--I never experienced any lag or performance issues. A button for ending the game would be beneficial as I had to ctrl+alt+delete out, but that's okay for a jam. Overall really good work.