ok so i have a ton of things to say hope you don't mind
First off, the difficulty, I love it. Hard games are pretty cool, and you nailed the difficulty, it is not too hard, and not too easy. However, it can be really unfair sometimes. This is due to the overall gameplay.
So, whenever the character walks, there's some sort of delay. First he start by going slow, and then suddenly he gains a real fast speed. Since bullet-hell like games require a good movement precision, the character should just start walking in the fast speed, or always walk slowly.
About the attacks, they're nice! It's just a bit sad that it slows the character down. Here's a little suggestion: If you're looking for a fast-paced chaotic bullet-hell, how about the attacks just don't slow us down at all? It would be seriously fun, and that would allow bosses to be more difficult, since you can now focus more on dodging. (Heavy attacks should slow us down tho, since its heavy)
The bossfight. Man, i love 12 string. He has such a cool design! Here's some suggestions for the bossfight: There should be a sound to indicate when he's going to fire his snipers, it would be really helpful. Also, the second phase was awesome, i just think we shouldn't be able to damage him when he's switching phases, i killed him before the bullets could hit the ground, which was kinda sad.
I also think it would be nice to have some dialogue. Well, not exactly a dialogue, just some sentences that the boss says before a fight, for example, "Time to go wild, comrade" (sorry im not good with those) It would really add a ton of personality to the bosses, and make them more enjoyable.
Overall, this little thing here has so much potential. Don't stop working on this game, i believe that this could become real, real fun in the future, so don't give up :)
btw nice funi cigaret