Heckin' sweet game! This game is all that and a bag of chips, well-polished in all aspects. Great art and presentation, charming concept, satisfying beat-em-up combat, bosses with tons of cool patterns and phases, and so on and so on: it's a smash hit to me!
But of course, there were some aspects I'll give some feedback on nonetheless (though they are minor nitpicks considering how well-constructed the game is already and how much fun I had):
The controls were a bit wonky to learn: no tutorial or anything as it just dumps you in combat, and a bit odd that you don't switch the menu prompts from gamepad key icons to keyboard key icons to reflect whatever is used at the moment, and also I feel like Z/X is used more nowadays for actions than A/S for keyboard (and why use A/S for combat but not A/S for menu navigation, instead making it A/B?).
The bosses did feel a bit frustrating at times in many respects. Many times they did not have good enough telegraphs: sure, the big moves like the laser had telegraphs, but moves like the beard poke and skull fireball just come up whenever they feel like it. Speaking of the laser, moves like that and the cat felt way too punishing: once you get hit, there is no recovery from it I could find, you just get your entire health bar destroyed with no way to get out of the combo. Also, a lot of the bosses had weird periods of invincibility which didn't make sense: felt like it was annoying that not only were they invincible when attacking, they were invincible when preparing to attack too. I realize many of these things might be on purpose to capture the old-school beat-em-up feel, which was very mashy and damage was largely unavoidable as to get kids to spend quarters upon quarters. It's just a little strange and unfair to get used to, since a lot of beat-em-ups nowadays highly favor big enemy telegraphs and such to allow for more skillful no-damage runs (though I think it's still possible to beat this game without getting hit, so it's not that unfair or anything).
Again, thank you very much for this wonderful game!
EDIT: Have been able to beat it now without even dying: bosses are definitely a bit more fair than my initial impression of them, just gotta get used to it. Again, well done, and love the classic Ryu 'uah uah uah' defeat scream echo, haha!