Well, sorry but I'm not gonna try beating the hard versions. Like the game and the challenge but forcing me to watch boss intros for over half of the overall play time isn't cool. It should be a dead giveaway that the unskippable intro takes what close to ten seconds and then you can die in way less than one just the repeat the whole thing again. In difficult games especially trying again need to be quick as hell.
By the way, from those three first levels, the second was easily the most difficult one. I struggled with it quite a bit and after that the third one felt like a breeze.
You were kinda breaking all the cardinal rules of difficulty. First of all, it was very unfair in many ways. The sides of the play arena were like a minefield. Go there with your own risk. At any second something might spawn right next to you without a warning and instagib you. And the key here is the "warning" bit. The incoming attacks would need to be telegraphed somehow. No need to tell what is coming but just marking the positions a bit before they were going to shoot would be awesome. You could have used the boss for this easily or then created some own individual sprite for the purpose.
I think the game might have even worked better if the attack positions weren't randomized but designed. At least then you could always just force your way through by memorization and sheer will. And there wouldn't be this much of those "crap deal hands" that are just straight up unavoidable. At least the bigger fan of bullets at some angles was just not dodgeable.
The second part of not being fair really isn't even that but not seeming like it. It's something I still haven't gone trough a jam without telling someone, the size of colliders. The need to be smaller than the actual sprite to "seem" fair. The human eye is not as accurate as computer especially in the midst of hectic struggle for survival. And feeling like you didn't get hit when you still died is like the worst feeling ever. This also has additional boon of allowing for more close call survival situations where the player should have died but didn't due to your benevolent will. And those are always fun!
A slight acceleration might have been nice to have on the character. Right now it was very hard to make small precise movements. Or another way to solve it would be a Touhou like slowdown key. Also in Touhou series the slow key shows the actual collider of the character which is like a size of a pixel.
Then we come to visuals. Didn't think I'd ever say this but I think there was too much bloom. Other than that, the juice was pretty much on point. The camera shake was kinda spot on (I usually like to add some angle too, makes it look even spicier). Sure the particle effects were a bit stock and bland but at least something was there and they got the job done.
Love the self irony, so you even realize yourself that that intro wall of text was too much...
Anyways, good job! 👍