I am so glad you enjoyed, I am honestly thinking about making this game more complete so people can really get into it.
Most of the issues you mentioned werent overlooked but instead a consequence of the lack of time (The irony), the snapiness, the boundary and even the boss, with exactly the same idea of appearing when the countdown ends (I made a sprite 
) But I had no time to implement.
The font and the music will probably be fixed as soon as the jam ends, again, I am really glad you played and enjoyed, thanks for the review, it was really helpful