I love shmups, they're one of my favorite genres to try! This is definitely reminiscent of Raiden, it's lots of fun to play. The ship moves a smidge too slow, in my opinion, and the keyboard controls are a little odd (I'd love to be able to use a controller), but the gameplay is still smooth and responsive.
The graphics don't quite give me a "SNES" feel-- but it'd be right at home next to some of the older Williams arcade games! The screen feels a bit empty without any GUI/HUD elements... I'd love to see a score increasing with every kill for that dopamine hit, or my ship's health so I know exactly how much trouble I'm in, heheh.
I love how you slowly introduced each enemy type one-by-one, then brought in the increasingly difficult combinations. The boss felt a bit underwhelming compared to some of the enemy patterns, I'd love to see more phases or attacks coming from such a massive battleship!
Overall, lots of the bullet patterns felt amazing to dance around-- with some balancing this could be an incredible bullet hell! I hope you continue work on it!