These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: Any zombie, really, since they can grab you and kill you instantly provided that you aren't at full health. But the nastier ones:
The armored zombies. They have helmet protection, which takes around three hits from the bat to remove, and have body armor that protects them from all forms of attack short of explosives. Finding them amongst a group of other zombies is a nightmare.
Exploding zombies, ones wearing propane tanks on their backs and gas masks on their faces. Sure they can't bite you and make you a zombie, but when they die (if it's not a super precise headshot), they explode, so killing them with the Cricket Bat is not an option.
Spitting zombies. They have more health than the average zombie, and they can spit acid at a distance. Not too cumbersome when facing them alone, but amongst a horde, they're insane.
Red zombies. Much faster than the typical zombie, and they can almost kill you in one hit! Act fast!
Game Breaker / Good Bad Bugs: There's a way to duplicate your items, such as ammo and health kits, thanks to switching from the storage locker in the safe room to your backpack upon exiting said locker, and touching the empty area on the right in the backpack inventory.
Patched now, unfortunately. But there's another one where the supplies in Brick Lane Market's street keep respawning even after you loot them.
Goddamned Bats: The rats and crows can make people pointlessly paranoid. And what they drop isn't really worth grabbing anyway.
A player-induced one in any empty zombified survivor. More experienced players farm places they've been to to hunt down zombie survivors for supplies, and the likes of the empty ones show up, occupying the position in the map that a perfectly good survivor could take instead!
Love It or Hate It: The critical reception of the game. Most of the things that the negative reviews found bad about the game, the positive reviews loved.
Narm Charm: "God Save the Queen" playing in the trailer.
Scrappy Weapon: The planks. Often too useless to carry around, the times when one actually does hold the line rarely involve doors, and there's hundreds lying around.
Animal meat and food in general fall into this too, when they take up too much space and the health they provide are insignificant (the meat can actually decrease your health too!).
That One Level: The "Arena", where all of your weapons are removed, you are only provided with a pistol and a few bombs, and the place is crawling with armored zombies.