That was enjoyable! I got past the first boss and was warped into an enemy-filled room. I got an error message:

___________________________________________
############################################################################################
FATAL ERROR in
action number 1
of  Step Event0
for object o_enemy6:

Unable to find any instance for object index '120236'
at gml_Object_o_enemy6_Step_0
############################################################################################
--------------------------------------------------------------------------------------------
stack frame is
gml_Object_o_enemy6_Step_0 (line -1)

I liked the style and the pace of the game. Things got a little frantic with all the bullets flying around, but I enjoyed it even though bullet hell games aren't my usual cup of tea. There were two things I think you could expand one to help differentiate it from the other twin-sticks.
1) Completely by accident, I held down the 'fire' button and it was in sync to the music. I thought it was intentional at first. Making a rhythm-based twin-stick would be an interesting challenge and could open up some interesting possibilities.
2) I really liked that you could reflect enemy bullets with your melee attack. I'd like to see that expanded on, perhaps even made it into a major game mechanic.

Keep up the good work!