I think I've said this on other games already, but rhythm games are something I wish I knew how to do, so I always appreciate seeing games made in that genre.
As a SHMUP, it's pretty solid. As a rhythm game, it feels a little light currently. I had a lot of trouble really getting "on-beat". The ever-ticking metronome was unfortunately a little monotonous from an audio stand-point. Still, I think the idea overall is very solid. If you could make the shot-timing a little more satisfying, I think this could be really good! Maybe even incorporate some power ups or other bonuses for sequences of well-timed shots!
The story has potential, but seems like a bit of an after thought in this version. Since it's a jam-game, that's understandable, but I do appreciate story & context when playing a games, even short ones.
The graphics are nice and colorful! If I had a critique there, the background is so vibrant that it kind of blends with the enemies and other "active" sprites sometimes, making it a little hard to read the action. But it wasn't so bad that I got into trouble playing or anything.
Overall, I think this is a cool idea with a ton of potential! Great work, I hope you keep working on it!