TLDR: it's just a boring grind fest that only gets worse the more you play. needs way more polish or a reason to play for more than an hour.

they really need to make it so you can rebuy the damage, health, or sprint upgrades for each night to stack upgrades. some way to make the nights pass by faster cause it takes so long. reload speed would be nice as well. right now there isn't any added gameplay from night 1 to the rest of the nights except for more monsters. some sort of pack a punch, gun upgrade system, or just something to make you feel strong past night 1 would instantly make this game more fun.

the only saving grace is the last round and sock monster rounds which are actually pretty cool and unique, but the game's systems feel like they're fighting against you even during those rounds. sometimes you'll be completely surrounded on the last round if you get an unlucky spawn area and you just have to jump like an idiot or you insta-die to the guys running at you.

another gripe with the game is that the hitboxes are genuinely awful. if an enemy is attacking you, you cannot shoot them. you have to take like 5 steps back before you can shoot them. objects in the game have terrible hitboxes so you're shooting walls half the time if you're trying to shoot near an object.

100% update:
the 100% is a slog and is not fun. the last 2 nights are literally 2 hours long. the enemies become bullet sponges and you need multiple shotgun shots to the face to kill just one guy. would be a better experience if the achievements ended at 3 nights. it's so dumb that the most optimal way to use your level ups is to wait until you buy the health and sprint upgrade so you dont waste points on those. could be way more interesting level ups like damage, reload speed, shield.

also stupid that the game forces you to stick near the door half the time when the map is so cool looking. and then the game gives you speed perks which don't really matter if you're hunkered down near the door. why not add stuff to help you protect the door like turrets or something.

i played zombieville usa 3d which is similar since it's also an arcade shooter, but it just felt way more cohesive and it actually gave you fun goals to work towards with the mastery weapons you unlock that look sick and are very strong. having a fun upgrade for your weapons is so sick and makes the last few hours of the completion fun. literally just change the bullet tracer colors, bump the damage up, make the reload faster, and invert the weapon colors and bam you have fun upgrades for your guns for people to experiment with.