I just started playing, and I have to tell you I think the music is awful. It's really super grating, loud and just throwing noise in my face - you don't have to have this constant loud snare drum beat going on all the time, a little light synth would get the point across just fine.

Great job, man. I just really, really would love it if you added some different weapons and enemy behavior - I feel like you're so close to even better gameplay. It stands out in the Arena that the enemies don't react to you at all, it would be so great if a few of them tried to aim at you and avoid your shots or something.