I love the steampunk aesthetic, and this game really delivered for me. I've seen at least a couple games already with the changing weapon shmup mechanic, but I think your game does the best of the ones I've played. All the guns felt distinctive, satisfying in the own way, and crucially, forced me to change the way I played in order to use.
The only big disappointment for me was the audio. I actually ended up turning my sound off completely because I found the sounds to be really grating even with my audio turned to its lowest. I also just felt that the sounds didn't match up well with the steampunk aesthetic.
Nice work though, overall I thought it was great! The aesthetic is beautiful and the game is fun as well.