This is my first post here but I've been playing this since a little before alpha 15 and have come up with a few suggestions that I hope haven't been repeated elsewhere.
First, make higher tiered doors require power to work, so like the vault door (maybe only the v3 version or a derivative thereof), the reinforced draw bridge, and the rolling garage door. Mostly, the idea is to make them more distinctive as high-tier building materials, but also because vault doors can be kind of cheesy if you can place them everywhere and cost relatively little to make.
Second, eliminate beaker requirement for chemistry station, but make most of the recipes (meds, gas) require crafting implements like the beaker. The idea is to make getting a chemistry station less dependent on RNG gifting you with a beaker, while also still gating some of the more overpowered items. Additionally, this would go hand-in-hand with eliminating crafting of items at other stations (i.e. campfire glue and gunpowder) for streamlining purposes. Could probably add another implement (i.e. retort flask, some sort of mixing machine) to make crafting faster or perhaps to enable large-stack crafting.
Third, make liquids work more like a forge resource. When interacting with liquid-containing objects (i.e. toilets, jugs, etc.), you have the option of drawing liquids from the object or filling it up if you have jars in your inventory. Only one type of liquid can be filled into any given object at any time.
Fourth, add a tendency to dig to Dog AI. Rather than slamming against solid obstacles, perhaps dogs could be made more likely to dig than human zombies? They could also have higher multipliers against dirt and gravel.
Fifth, make firearms malfunction. Now that firearms are easier to find and use, I think that they should have additional drawbacks. So with lower quality firearms, you have a higher chance of malfunctions, forcing you to reload the gun. With level 5 or 6 quality firearms, chances of malfunctions would be non-existent.
Additionally, here are a few various ideas for blocks/objects and items.
A few block/object ideas:
Iron stove. Faster at cooking than campfire and can use all the same fuels as the campfire. Less heatmap generation as well, but very little light.
Electric stove. Equivalent effectiveness to iron stove, but requires power connection. Even less heatmap generation, but no light at all. Crafted at work bench.
Dehumidifier/Water distiller. When powered, generates roughly two jars worth of murky water per day. Crafted at work bench.
Double doors. Self-explanatory. 2x2 double doors in all styles.
Hotplate. Simply put, it's a tile that heats up when powered, causing damage to any zombies that walk over it.
A few item ideas:
Pneumatic power fist. Self-explanatory. Normal function would be like a regular steel knuckles with more damage but slower swings; charging attack however, would be damaging enough to break rock and metal in a few strikes like a pickaxe or sledgehammer.
Bangstick. Essentially a spear with a shotgun charge on the end. Single use: can be thrown or thrust, and stacks up to three per slot.
Tomahawk. Variation on steel axes, with better entity damage at the expense of block damage, but just as efficient at harvesting. Likely to dismember or decapitate.
Warhammer. Similar to the above, only for picks. Armour-piercing.
Trench tool. Similar to the above, only for shovels. Causes bleed.
Basic/Advanced item repair kit. Former for basic items (i.e. pistol, double barreled shotgun, rifle, tools, iron weapons) and latter for more advanced ones (i.e. marksman rifle, chainsaw, steel weapons).
Also, a few enemy/fauna ideas:
Diseased One. Zombie with blackened spots of skin and missing eyes: attacks have a much higher chance of infection and can inflict a poison debuff which drains stamina and health. Probably would mainly spawn in hospitals as sleepers. Poison could also probably apply to the snake as well.
Mutant spider. I always found the spider zombie to be kind of awkward-looking and think that an actual spider would be a better fit in that it can also jump and probably would be more easily animated for climbing walls. Could probably hide directly on ceilings as well. Spider zombie could still be in game though, maybe as a faster zombie that can also jump.
Pile of infected viscera. Less an enemy than a block or object type; looks similar but not identical to regular gore blocks. Getting too near will cause it to explode, not only damaging the player with a chance of infection but also alerting nearby zombies and driving them into a frenzy.