I don't know what it was, but the exploding into shards of glass sounded cool and satisfying to shoot the enemies.
(might not have been implemented) but I never had an option to start a new game, the game would stop on the game over screen and I'd have to close the app to play again. Maybe something simple like clicking esc/start when on game over reloads the scene :)
Also the very first enemy on each wave was always really annoying haha since there wasn't much time to react.
Lastly, I found the pause menu nice and creative. It's much easier to focus when there's only one option on screen at a time which I liked :)