Hey, so, I understand the game has some pretty big issues but there will be no updates for this as it was a jam game.
But here are some answers either way:
The game is actually being rendered at 64x64 so there's no shader for that going on, if it were an actual serious game project, there would be an option to turn this off.
Yes, I noticed some enemies getting stuck as well.
The hitbox is not very advanced and does not cover the sprite or anything like that, it's just a 2D top down box or circle, can't remember right now, but same answer here, these would be fixed if this was a real project.
The "C" button, did not turn out that useful except maybe if you have low life, so I mostly agree there.
There are multiple weapons available on Level 3, they are just hidden, but sure, there's probably too many enemies either way.
Yes, saving would be nice to have but it didn't make it in, once again, if this was a real project then I would 100% have saving of some sort.
And finally, as stated above, there won't be any changes made to this so the bug will have to stay.
Anyway, thanks for trying the game and the feedback, even if I won't change anything. :)