Really do love the art style, but needs work as you know. Really do hope you'll consider continuing work on it. Some quick feedback on what's currently there;

• Player gets 'caught' on doorways (slows down for a moment), I think the issue is the player collider is around same height as them, making doorways slightly taller should hopefully fix that
• Disable the enemies collider the moment they die, currently there's a short delay which gets a bit annoying and can get you killed (corpse blocks retreat)
• Make the damage indicator directional, so it's clear if damage is coming from sides/rear. The claw marks could simply be closer to relevant edge of screen
• For the semi-auto weapons, allow the mouse to be held. Having to spam click is not easy on figure.
• I feel shotgun should be rebalanced feels a bit to weak at the moment. Either increase it's OHKO range as currently it seems to only work at point blank, or change it up to be a crowd control weapon (wide spread, and bullet penetration)
• Didn't really notice a difference between the two pistols, is there any point to having both?
• Everything needs audio feedback, like picking up ammo
• Angle of the tommy gun sprite was a bit odd.
• Levels have too many tight corridors, needs more more rooms and maybe some wide corridors.
• Really needs a map (with fog of war), so player knows exactly where they've been. Unless you plan to revamp level generation with landmarks and themed zones.
• Have mouse wheel cycle through weapons as well
• It'd be nice if there were more persistent battle evidence; enemy corpses, bullet holes, bullet casings, blood on walls