I think the mode could benefit from a few changes, especially more rooms, difficulty scaling, and a rebirth system.
I’d also suggest taking another look at the damage system for melee weapons, shotguns, and explosives.
For melee weapons, the damage multipliers between body and head seem way too extreme. For example, a hit to the body might deal around 33 damage, while a head hit can deal around 800. Since melee attacks and explosives are much more likely to hit the body than the head, they end up dealing very little damage in most situations. I think the body multiplier could be increased and the head multiplier reduced to make the damage more consistent.
Shotguns have a different issue. If a shotgun fires, for example, 8 pellets, the game seems to detect the entire shot as only one bullet when calculating the damage. This means that even if all 8 pellets hit, the weapon may only deal the damage of a single pellet/shot, effectively making it deal around 1/8 of the damage it should.
Meanwhile, single-projectile weapons like pistols don't have this problem and can deal their full damage consistently. This makes them significantly more effective and, combined with speed buffs, encourages players to simply rush through everything with pistols.
Fixing the way pellet hits are calculated, while also balancing the body/head multipliers for melee and explosives, would make the weapon balance much healthier and give players more viable options instead of heavily favoring pistols and speed buffs.