Extremely fun, and difficult at it. I will admit, getting past the arcade machine on Hard is not possible for me (some attacks are too fast/pulsing for me to see them properly >.<), but Normal and Easy are doable. Thank you for the option to choose difficulty!
The difficulty is a little out of place place, I think, for certain bosses. The arcade machine feels extremely difficult for a 4/5th boss, with that wavy attack pattern (the green and violet one), but it's not a deal-breaker. I think it might be just me being bad at the game :P
I really love the designs of everything, from the menu itself to the bosses, and the simple but catchy music. The sound design can feel a tiny bit irritating later on, but nothing serious. I really like that you show the player's actual hitbox within the bear sprite, too (Why didn't we think of that lmao)
The upgrades feel very natural and rewarding, and I like that you lose them in stages rather than all at once when you get hit.
I think the only thing this game is missing is a health bar for the bosses. You get a feel for them after a few playthroughs, though.
Overall, a definitive 10/10, no questions asked!