I'll use this thread to collect my thoughts, as I've played this non-stop for several weeks and want to forget it for a while.
The first thing to know if you've heard about the project before is that yes, it was in development hell for many years, but is now (as of version 41) a fully featured game with enough to keep you occupied for a long, long time. It's still in active development and will likely receive an even more comprehensive update with version 42, which promises interactable NPCs. This will change how the game plays at a fundamental level and on the whole I welcome the changes, although not without reservations given the devs' reputation for spotty programming and inconsistent approach (the game still lacks basic things like sitting in chairs and animations for opening a car hood). The game was mostly written in Java, so I'm skeptical about the feasibility of some of their ambitions.
If you haven't heard about it, it's basically a real-time, isometric, keyboard and mouse controlled survival crafting and survival horror hybrid. It's heavily inspired by, but not as deep as CDDA, but also adds different elements. The fact that it's real-time, as well as its delicate control scheme, where you control movement direction with keyboard and facing direction with the mouse, makes the game challenging not only from the POV of player skill, but also their ability to maintain a cool head and make right decisions on the spot. Faced with a zombie ambush, your hands will turn to jelly and you'll fuck it up. One scratch, you might be infected; if it's a bite you're dead. You'll die many, many times and this is how you learn. With every death you learn something new.
The words that flash before any new game is "This is how you died". That's the premise of the game. The situation is hopeless and you're just some regular Joe who is putting up a fight despite the odds. There's no end game, no cure, nothing to save. In the beginning you're unlikely to last a day in "Survival" mode, then you'll slowly begin to last longer. You move up to "Apocalypse" difficulty and repeat the process until you create your first survivor that lasts a month and finally becomes self-sufficient. Disappointed, you start fiddling with the "Sandbox" settings, making the game as hard as possible. Soon you'll be dealing with sprinting zombies who have superhuman strength and toughness, extra rare loot and all sorts of sadistic little details to make your life miserable. It's part of the development arch of any Zomboid player to become a fiend for punishment until they find a happy medium.
The versatility of the customizable settings in "Sandbox" mode is what adds longevity to the game. You can customize number and physical characteristics of zombies, rarity for different kinds of loot, availability of running water/electricity at the start, temperature and humidity, etc. Mods exist to further extend the options at your disposal. Some of my favorite mods, which I now consider indispensable:
Customizable Zombies - lets you specify the exact percentage of different kinds of zombies. I like playing with a minority (~10%) of sprinters, just to spice up the game without making it hellishly difficult (and repetitive).
Filibuster Rhymes' Used Cars! - greatly expands the selection of vehicles in a lore friendly way. The cars have more variety and are usually of much higher quality than the native ones. Safe to use even by newbies.
Cryogenic Winter - makes the weather a much larger factor in your gameplay. You'll freeze to death in the first day if you don't find appropriate clothing. I like to modify the LUA settings to make the weather very hot in the summer and very cold in the winter, although it's unlikely for any character to see the change of seasons.
I eventually grew tired of the game, as there's a lack of challenge in the late game compared to the first week. Once you become self-sufficient (usually involving the combination of defensible base, working car and generator) the game gets boring, as there's no reason to explore and you know you can only die if you commit a stupid mistake. At that point your death drive will make your character take unnecessary risks and you'll die a stupid, unfulfilling death.
Without going too much into specific mechanics, suffice to say there's enough variety to keep you entertained for a while. You can live your fantasies as a crazy axeman and zombie slayer, make a living from foraging and fishing, be a mechanic that fixes cars and drives around exploring the map (driving a car is surprisingly rewarding, specially after you've gone through all the trouble of geting a working one), etc. You can also do boring base building and Stardew Valley shit like farming, although I'm not sure why you'd want to do that.
One of the best things about the game is that the map is HUGE. Whether you prefer urban survival or a quiet life in the countryside, you're unlikely to see half of it in a single playthrough. Traveling between towns can feel like a real adventure.
I'm anticipating the release of the NPC update as I think we'll finally be given objectives to work on after we got our own base, car and generator. More variety in enemies and more dynamic events that add chaos to the playthrough would also be welcome. There's a popular Helicopter Events mod on Steam Workshop, but IMO it just adds arbitrary nonsense that clutters the game. I think I'll wait for version 42 before I give this a new spin.
CDDA is the better zombie survival crafting game, as far as those go.
Zomboid has some very odd design choices, like the "one bite = death" mechanics and zombies that will go after the player regardless of circumstances. I tripped the alarm on a house and instead of the zombies running towards the sound they all converged on me, despite being elsewhere at the time.
From my experience, zombies will converge to the origin of the sound or whereabouts, but if they locate the player they will chase him instead and move to the point where they last saw him. They also seem to have heightened vision when alerted. The best strategy is to leave the place as fast as possible in the direction of least population density.
You can also disable the infection mechanic in Sandbox, but the game is unlikely to provide sufficient challenge/tension in that case.