That was fun ! I felt like I could not go any further than what I did since monsters just spawn more and more until a point where there are just no other option that just dying, but otherwise it was cool.
The game is too slow, not only the pace, but the overall feeling : you could make the bullets twice as big, the fire rate 5 times faster, monsters come more but kill them in a single blow, and it would feel like you're really doing a pure rampage. Here, you are surviving, which is great, but does not put the emphasis on juice enough in my opinion.
Also, small detail but I did not understand the yellow powerup.
Thanks for the game :)