I think this is purely the most fun I've had in any jam entry so far!! Not only have you executed the idea wonderfully, the amount of polish already makes it feel like a near-to-release game! The first few rounds were a bit slow and repetitive with the shooting SFX (as others have mentioned), so adding some random pitch variation to each shot or creating some new shooting SFX to pick between would add a lot. This isn't as much of an issue in the later rounds, tho, as the sounds from the siblings add some complexity and randomness. I also found the player's gun to be too powerful in the later rounds as I could essentially one-shot the green squares (which I assumed to be tank enemies), so that might be something to look at. As others have also said, there were some slowdowns later on which may be a result of the browser, so maybe some optimisations could be something to look into - I'm assuming it runs better as a standalone application, tho! ^^
I absolutely LOVED the small details when each enemy was shot and the multiple sprites you drew for each of them, it really adds a lot of charm to the project!! The particle effects also add a bunch of juice and the geometric + pattern theme was implemented in the best way possible. And, without the time constraints, I'm sure you'd want to add some music and possibly boss fights/waves and extra game modes, but you've already done so well with the progressive and interactive tutorial throughout each round!
I'm even happier that I could beat the game! >:D Amazing entry, and I really do hope you continue with this project! It surely has a lot of potential, and you're making me want to make a game similar to this now ^^