Hah, love it. I really enjoy the style of the graphics - colorful and true to the retro spirit of the game. I think you could stay with the same color palette but may add just a 'hint' of shading to make it a little more dimensional, but do it in a way that is absurdly cheery, everything should look like hard candy or one of those ridiculous Lisa Frank trapper keepers from the 90s (see https://www.google.com/search?q=lisa+frank&rlz=1C1GCEU_enUS844US844&sxsrf=ACYBGNSC-L-Y3k8xA3-20cjh5KhVz3Or5g:1580495155586&source=lnms&tbm=isch&sa=X&ved=2ahUKEwj-nsWiu67nAhWJBc0KHQGTAksQ_AUoAXoECBMQAw&biw=1509&bih=1039 for examples)

I thought the music was really fun and fit the game well. Absurdly upbeat when gunning down clowns.

I had some trouble understanding the control schema for a moment but caught on after I exited the game a couple of times accidentally when hitting the ESC button. I would flesh out the UI and navigation more. At least add a main title screen that you can back out to while hitting ESC and not simply exiting the game.

The game is challenging, and maybe too challenging for me - I find it a lot less forgiving than say a AAA title like Doom 2016 where you have a fighting chance and aren't immediately killed when you get bumped. My reaction time isn't what it used to be, I would maybe ease up on the difficulty or have the opportunity to refill your health - I wasn't able to get very far. The enemies are fast and maybe a little too much so. I would like to spend more time looking at the levels but I get killed after like 30 seconds.

In any case, I think it's a great start, and with some fine tuning you could make it an enjoyable little experience. Slap it up on Steam and make a few bucks in the process.