Really nice start!
Feedback:-The game feels pretty good to play, and I like the enemy designs so far.
-I like how the beam enemies interact with asteroids and those diamond shaped enemies which deflect the beams in another direction. The only problem is those diamond enemies seemed to either be indescructable or took a lot of hits, so there were many situations where (since they made the beam vertical) I had no choice but to fly straight through the beam and take a hit, as two of them in conjunction would create beams that covered an entire vertical area of the screen.
-Since most of the enemies took only one or two hits to kill (which is good), the missiles didn't seem to be that useful until the boss, which meant although I got a second weapon in the first level, I had no incentive to use it. On one playthrough, I got two extra weapons in the first level, which I think should be the norm, to give the player a bit more choice right away as to which weapons they use. (also, maybe make the missile have an area-of-effect type thing, where it will explode upon hitting an enemy and also destroy nearby enemies. That would make it more useful in non-boss areas)
-The first boss's beam weapon was annoying, and basically made it so most of the time, it wasn't safe to be in the area in front of the boss, which is the only area you can shoot it from. Never beat the first boss.
-I would make collision more forgiving. Most bullet-hell type games have a "magic pixel" where you only get hit if a bullet collides with the very middle point of your ship. While this isn't quite the level of bullet-hell, it would be nice to allow for more near-misses, which was especially hard considering the size of most enemy projectiles.
-I would lower the saturation of the background. That blue-green nebulous mist made the screen more busy, and made it harder to read.
Anyway, other than that, I had quite a bit of fun with this game so far. Look forward to seeing it develop!