Madmole, there was a topic not long ago about zombie biting that got me thinking.
Right now, melee has some dangers attached to it - infection, stun and bleed, rage mechanic and of course chance of getting whacked. But unless you play with always run or on insane difficulty (which I dont, because bullet sponges are really not my thing) unless I step on the landmine I never die. In full heavy armor I can be pretty careless and still get away with it 99% of time.
Getting swarmed should be much more dangerous. I remember one of those rare times that I actually died, while exploring the lvl IV PoI with the secret base under it. I was creeping through the library, when I managed to wake one of the cops guarding the place. He destroyed a block right under me resulting in me falling down into his swings. He pressed me against corner and I panicked, tried to run away, but there was no escape. He smashed me into the ground.
That is how I imagine zombie being dangerous. If they swarm you, its you either fight them off, or die. No chance to run away. It is the same, when you fall into the trap in some of the PoIs, this intensive life or death situation, that in the end makes you careful. The game should severely punish you, if you are not careful and well prepared.
SKIP HERE FOR THE IMPORTANT PART
What I propose is new mechanic for the zombies - knockdown. It would work like this.
1.Zombie has a chance to trigger a knockdown with each hit. Being hit from behind would be almost guaranteed to knock you down.
2. Play death animation (or getting run over by your own vehicle animation), keeping the camera inside the player character.
3. Zombies use eating animation to attack (you can see those animation if you die)
4. Pinned down debuff would decrease resistance to being knocked down to 0. Any damage will prolong the effect, effectively keeping you on the ground untill you dispatched all the zombies
5. (Optional) probably a bit harder to implement, but being knocked down would limit your options to some smaller arms like knife, pistol or a club. Sledgehammer, spear and rifles would be unusable, increasing the value of sidearms.
6. Once all zombies are dead, the debuff would not be refreshed and player will stand back up.
Larger zombies and animals would have higher chance to knockdown. Especially bear hits would be guaranteed to.
I think that all the things are in place (animations, rezistances, status effects etc.) so it should not be very hard to implement. Of course I dont know your code so I might be wrong.