Ah man, this game was fun to play! Incoming large text wall :P
Initially I had played it on Android (Moto G Stylus 5G, with 4GB of RAM) with a Switch Pro Controller, and it ran smoothly until I ran into large packs of enemies (similar to the HTML5 version). Although I could only get halfway into the second level on controller, the game was fun enough to try with KeyBoard/Mouse, and I got up to the boss on the HTML5 version! I didn't beat the boss, but hey, I got to see more of the game!
~ Undermined Gripes ~
I found it difficult to play with only stick controls, but that's a skill issue on my part (I usually play with stick + motion controls - thanks, Splatoon). In addition, because I was using a Switch controller, the A and B buttons were swapped in function, but it's whatever. Whenever the game got too laggy, my sword swing inputs wouldn't be picked up -- I probably could've avoided the frame drops entirely by running the game on my actual computer/better hardware, but I could manage with KBM in my Chrome browser.
There wasn't anything that I couldn't find a workaround with, and I never ran into any major/minor bugs - it was generally a smooth experience. That being said, to anyone else who cares about it, I would mention that the NSFW content in this game is a bit lacking (there were some odds and ends placed in the levels, and the rest I assume is behind Extras), but, then again, this is a game where you need both hands to play ;)
~ The rest of this feedback is positive ~
All in all, this was a short-and-sweet game to play! I found myself using the sword to deal with most enemies, weakening tougher enemies and finishing them off with melee, or picking off ranged enemies with my shots. It was very fast and fun, and to someone who's never played Ultrakill, it kinda reminds me of that - weaving through ranged attacks, always on the move, and closing in for the health bonus. I would love to see another game like this, with more controller/touchscreen support; this was a fun way to spend two hours of my day.
Btw for anyone else reading this who's interested in downloading the game - don't worry about the "unsafe/untrusted" program warning that appears before running or installing the game. The only thing this game will cost you is your time (which isn't much) - and maybe some money, if you're down to donate (which I definitely advocate for)