Thank you for playing and the detailed feedback!
About the shooting while spinning/dashing: originally I didn’t allow shooting during that state mostly because of animation limitations, and then I started designing around that restriction intentionally. My thinking was that there generally shouldn’t be situations where you need to shoot while mid-air spinning, and that sometimes trading combat options for mobility could add a bit of decision-making during fights, along with the fact that some things can only be damaged with the spin. That said, I do understand your point about it sometimes feeling like the game is ignoring your input rather than challenging your execution. Even if the mechanic ends up staying the same (I'll keep thinking about it) I'll at least add stronger feedback when a shot is buffered/blocked so it helps communicate what’s happening better.
As for enemy readability and interaction rules, my reasoning so far has been that some inconsistencies are acceptable if they don’t meaningfully punish the player or create situations where the “correct” interaction is unclear in a high-pressure moment. For example, with the mining penguins, I mostly treat them as movement tools/trampolines rather than combat targets (you could even sort of softlock yourself if you kill some of them). But I do think your point about clearer visual language is fair, especially regarding what is hazardous, destructible, or intangible at a glance. I have tweaked designs before because of this and will continue to do so in the future.
On the difficulty side, you're right that the goal was never really “Kaizo” in the hardcore romhack sense. I mostly wanted to make something challenging for myself and a few friends who already play a lot of difficult platformers, while still being below the level of stuff like high-end SMW hacks or extreme SMM levels. In my head it’s closer to something slightly above the harder DKCR/DKTF content or more recent indie games like PsiloSybil, Zexion or UFO50. The in-game difficulty ratings are also relative to the rest of the game, not to platformers as a whole. So a 1 star stage isn’t meant to imply “easy” universally, but I can see how that could be misleading.
I have used the term “Kaizo” in some places because that’s how a lot of players ended up describing it (and I don't think it implies unfairness), but I’ve also tried to make the descriptions clear enough that people can gauge the type of challenge beforehand (now I'll add 'precision-platformer'). If I don't end up making it easier my hope is that the free demo at least communicates the experience more accurately than trailers or wording alone probably can, so people don't spend money on something they wouldn’t enjoy.
Anyway, I appreciate the thoughtful critique.

