Super fun! Loved the music, SFX and the graphic style of the game. The mechanics were simple yet creative, and basically everything you need. Would've preferred a bit larger arena though. Maybe in the future updates (if you choose to continue developing the game) the game could have different arenas with potential environmental hazards, like moving spikes or lava pits. The fact that you HP is also your ammo was a great idea! One thing I'd focus would be making the dmg-dealing elements a bit clearer, since for me at least it seemed that the red dots from the exploding boxes didn't deal dmg but used the same color as the bullets. Big ups!
We'd greatly appreciate if you checked out our submission! :)