Pretty nice mechanic and really smooth controls. Didn't find any bugs at all, well done! Sadly I couldn't get pass the 2nd boss after 6 tries. I guess it was too frantic, my eyes were looking everywhere (boss's color, bullet sprays, weapon box, weapon equipped).
So I guess here are some ideas you can use; add mouse scroll to change 1-2-3 weapons, weapon from exchange box directly goes to player, health packs, maybe a less intense color for incoming damage (yellow, transparent or just outline maybe), and lastly the boss could take a breather.
Other than that I really enjoyed playing against the first boss, it was challenging too, had me on 1 hp sometimes. The music, sfx sounded good too, so I think you did well overall.