Some quick suggestions (Note played the web player build)
Gameplay
- Needs to be able to zoom in, quite hard to get headshots when the target is so tiny on screen. You could just reduce the main cameras FoV on key press or do it the fancy way with a picture-in-picture scope (second camera with smaller FoV, that gets rendered to screen with a circular mask).
- Hit responses; The big zombies should react to being shot so it's clear the player is doing damage, both pain animation and blood. Body shots should cause enemy to flinch, maybe stun them a moment. Also head shots really aren't satisfying, find a suitable sound effect and show exaggerated gore effects.
- Vary the firing round, simply randomizing the pitch a little will help (like between 1x and 1.2x)
- Rocket feels too weak for what it is, larger AoE would be nicer. Also a more impressive explosion effect
- Tractor is quite weak, maybe switch it to being a combine harvester with much wider damage area, but with a long cool down. So it can be used to clear zombies away from fence if needed. It'd also be interesting if you added more farm themed 'special attacks' like it (You could use Call of Duty's killstreak rewards as inspiration), each with their own cool down/limitations.
- Zombies need an attack animation, so it's clear they're damaging fence and house.
- Fence should visually indicate it's health, have the model swapped out with damaged one as it gets lower. Ideally multiple stages, like 4 variants. As well as have particle effects/animation as it takes damage.
- You should probably borrow elements from typical wave/horde shooters. Spawn enemies in waves to give player a chance to breath. Between waves have upgrades to unlock/buy and maybe let player pay to repair fences.
- Rather than constantly spawning enemies from all directions, for balance perhaps you should start by spawning them from one side, then as it progresses change which side and add more sides till it's 360. This could be tied to waves.
- House taking damage should have sound and visual effects (house shaking, dust particles)
- Persistent evidence of combat would be satisfying to see, I understand piles of corpses would be performance concern, but perhaps you can at least leave blood stains.
- Shooting enemies attack house walls is slightly awkward, not sure best way to approach this though. Maybe design house so player can see walls from side, so like a '+' shape house layout, where player can stand on a tip to shoot at two neighboring sides (Like historic bastion forts).
UI
- Instructions menu does not show what key it is to return to main menu nor does it have ui button to do so
- UI is quite small (2K monitor), I assume it's not scaling with screen size
- Need setting to change mouse sensitivity, this really is a must for all FPS
- Ammo really should be somewhere easier to see at a glance, like next to crosshair. Could also have a last round in magazine indicator, like a different firing sound (like shot followed by a click).