I finished State of Decay, I enjoyed it, and I would recommend it--but with some hesitations. The more I played the game, the more it felt sort of rote and a little tiring. It feels like the developers built a great core gameplay loop, but didn't do much to add to that.
The way the game works is thus: You have a base stocked with survivors. As time passes, the base uses up resources. So you go around a few towns and surrounding countrysides, break into houses and warehouses and the like, and steal stuff. You'll find both items that your character can use, and resources that your base can use. You carry regular items in a backpack, which has both a slot and weight limit after which you get encumbered and tired more easily. Base resources are loaded into a large rucksack, which further encumbers you. If you can't carry everything at an area, you can send for someone from your base to run to where you are, pick up the remainder, and bring it back to the base. NPCs can get caught by zombies while they're making their way out to the looting point or while they're making their way back.
You can designate certain buildings to be "outputs". The game doesn't explain at all why you would do this, but the internet explains: the most important reason to do it is that an area designated a outpost spawns no zombies and is booby-trapped so that if external zombies move through, they get killed. You'll want to put at least a few outposts near your base to sort of create a zombie-free buffer. The second reason, which is not made clear in the game at all, is that if you leave base resources in an outpost, you will have a permanent daily allowance of that resource, which lowers your need for scavenging. By the end of the game I had a daily surplus of food and medication and broke even on fuel, so I only needed ammo and construction materials.
After a while your character will get tired. Fatigue lowers your maximum stamina. You can keep playing, but it'll keep getting worse. So you're advised to go back to home base and switch to another character. Likewise, serious injury lowers your maximum health. This is the game's way of forcing you to use multiple characters. This can be frustrating if you only have a few with good skills. Skills include cardio, wits (ability to search through things quietly), melee combat, shooting, and reflexes (appears to relate to combat) and they are leveled up by using them; someone who shoots all the time will quickly get a high level of shooting skill. At a certain point, once you've leveled skills, you can also select "specializations" for your characters. The game does not explain this, so it was about 2/3rds of the way through the game before I discovered this was a thing.
While you're out and about, you'll be asked to do missions. Missions could involve helping out neighboring groups of survivors, going to save one of your runners who has been caught in a zombie-infested area, helping to board up a building, climbing tall buildings to locate new sources of resources.
You can also find new areas to move to, as each base has different built-in facilities and different numbers of expansion slots. I only moved my base once, from the default church into a spacious and facility-rich warehouse. You can use materials to build different areas in your base; a guard tower, a garden, a medical tent, a research library, a cooking area, a gym/training area, etc. Some require particular survivors with particular skills to staff them, but most just give you a sort of passive boost. You can upgrade most building facilities. Ultimately other than areas that help survivors recover from fatigue or injury, I didn't really notice much of an impact from base facilities at all. It felt like another mechanic that was sort of neat but ultimately hollow.
There is a plot, but not much of one. At random, you'll get radio missions to go deal with various groups of people. There are military personnel who are here for an unknown reason, local small criminals and drug/weapons dealers, a group of friendly survivors, a courthouse serving as some kind of post-collapse civilian government, and a few one-offs. The actual plot missions themselves differ very little from the random missions you get. For example, taking the sheriff on a ride-along to clear out zombie infestations and save a trapped civilian is exactly like clearing out zombie infestations and saving trapped civilians.
Your player characters are basically randoms. You start as a camping dude named Marcus who has great default skillset. He's accompanied by a perpetual whiner who is useless named Ed. You meet up with an ex-military woman named Maya. Pretty much everyone else after these three are total blind randoms. There are five or six NPC voices that voice everyone; there's a wide wide wide variety of dialogue but little in the way of characterization. They do this because anyone can permanently die. During my first run-through, I lost both Marcus and Maya due to bad planning about 10 minutes apart 4 hours in. I was so gutted that I restarted the game. In my second and final playthrough, I was about 7 hours in when I lost Marcus on a routine errand. I considered restarting again. So they've done a good job of making the loss of a high level character pretty tragic. Marcus was my only loss that wasn't ordained by plot reasons on my second playthrough.
I guess I would describe my experience as sort of hollow. I loved the melee combat, which is quite complex and very tense (although poorly explained). I loved driving around in my car and opening my door to whack a passing zombie, or doing a donut and whipping a zombie hanging off the back into a telephone pole. But... I guess I never really felt like anything matters. I'd just wander around and scavenge (unnecessarily, my resources were never low) until I'd get a mission, missions were basically no different than wandering around in general, I'd play side missions until I got a plot mission, which were no different really. Occasionally I'd have to go back to my base to check on construction or switch characters. I was never scarce on weapons or ammo or meds at my base. I always had more than enough influence, the game's currency.
So in conclusion, I'd say that this is definitely a game that's worth trying, but that if you're like me, you might get tired of part-way through because there's not a lot of variation and much of the game seems a little like busy-work.
