First of all, Huge thanks for such a wholesome feedback!
You have nailed almost all the flaws I can see as well. Most of them are caused by lack of time unfortunatelly. Especially the balance. Also this is my first game of this type and it was really tricky to ballance that somehow (not just difficulty wise, but also the prices in shop and rewards per kill), hence I decided to make a trade off in making player slower and grow into bad-ass with time. I get the slow-issue from way more people, so this will be definitelly a thing to change as I am already working on a post-jam patch/update.
There are loads of things missing, one of them are death animations, that is why you might not notice that the 2-headed enemy spawns 2 little guys upon death. So he is supposed to be stronger enemy with 2 little anoying guys when you finally beat him.
I was glad I could get in at least some basic sfx and few music loops, but your points are totally fair, as well as with more abilities. Originally I wanted to have a skill bar with 4 different active abilities, but had to cut it, as I would not be able to finish that in time. Might revisit this idea again, as again, totally agree that this can get old pretty fast :)
Last issue is performance, I noted that into description as a known issue, but again, not much time to deal with it properly during the jam itself, I applied at least some perf optimization as it was even worse before, but need to work on this even more ;)
Again, thank you so much for this feedback, I love it, and when I finish the updates, I hope it will be only better and perhaps it will be a reason to revisit this little game of mine ;) Thank you!!