DayZ is a mod for a "realistic" shooter called ArmA 2, envisioned and written by Dean "Rocket" Hall as a game that more accurately depicts the zombie apocalypse.
His ideas for games very closely match my own; permanent death, real consequence for decisions, open world, emergent story, simple and harsh rules, and the wildcard of other players.
I enjoy games like this because only when there are real consequences to your actions do you actually feel emotional about the game.
Nethack is unrelenting and unforgiving, but it also has enough flexibility in rules that if you die, there was almost always some way out of the danger that you failed to think of. Yes, the game will try to kill you in brutal, subtle, and inventive ways, but those rules apply to you as well, and if you fail to remember them, you'll be smacking your forehead after your 20+ hour character dies with the object of his or her salvation staring you in the face. There is technically a story here, but much like Fallout, what you do in between story points is where the real story emerges. Because death is permanent here, you feel loss when your character dies.
Minecraft is a random world with simple enemies, simple rules, and no story. Yet this world has been more engrossing than any other game I've ever played. Your only enemy is the world you live in. You can do things to make this world safer, but it will never be truly safe because the randomness of the game will always conspire to create difficult situations. There are some in-game consequences here, but because you respawn (unless you play hardcore mode where the world deletes after you die) back at your bed when you die, that's not where the fun comes from. The fun lies in the exploration and finding rare resources. If you have a bad mining technique, you're going to waste hours of real world time, but if you come up with a new plan to optimize your discovery and it pays off, you feel good that you saved yourself time and became more efficient. The challenges within the game are waiting for you to come up with a creative solution, and it feels good to succeed.
Dwarf Fortress is an interesting strategy game where instead of controlling your workers directly, you merely issue orders, and it's up to the Dwarves to decide how and if they carry out these orders. This game added an interesting element for each worker by giving them experiences, relationships, and emotions. You are an overseer of some kind, and can check the status of your Dwarves' lives. If your champion digger loses his wife in a horrible smelting accident, he may not want to dig anymore. If you badly manage the resources and the Dwarves don't have any mead, they won't work as quickly or happily. You have to help your Dwarves survive and thrive in the harsh world, and when something terrible happens, it ripples through the community in unexpected ways. These rules and situations give rise to tales of civilizations which come crashing down because of some minor trigger, and always leave you wondering what kind of experience you're going to have when you start up a new fortress.
Recently, I was replaying New Vegas on hardcore mode (trivial additional challenge), and was advancing beyond my level (like normal), and got into a bad firefight. I realized I hadn't saved in ages, and was going to lose hours of my time if I my character died here. It was at that point that I started to feel panic and fear. I ducked behind a rock and tried to get pot shots off to keep them from flanking me, and scrolled through my inventory, looking for something that would give me the upper hand. Finding nothing, I had to flee on a broken leg, serpentining all the way, bullets whizzing around my head, and hobbling for my life. I breathed a huge sigh of relief when I made it out of that situation, because my lack of saving meant my actions suddenly had consequences, and my performance was going to determine if I had to deal with those consequences.
This is what I wanted out of my games. The emotional experience, not a canned story I trudged through. This is why DayZ was so appealing. DayZ takes all of these elements and mashes them together with the most unforgiving thing in our modern era: People on the internet.
DayZ starts you out with nothing on the shore of a 225 square kilometer area of towns and forest, and only asks that you survive in a world where zombies have taken over. You'll need to go into a town to get weapons, food, and water, to keep you living, but with those supply runs comes risk of being discovered and mobbed by zombies, and an increase in your chances to encounter another survivor.
What will these survivors do when you encounter them? That's a good damn question. It depends on the survivor. Because there are some healing methods that require another person, and two guns are better than one, it makes sense to team up with another survivor. But do you trust him? What are his motivations? Will he draw zombies off of you to save your life, or will he shoot you in the back of the head for your baked beans as soon as you turn your back?
There is no "leveling" in this game, only equipment. The entirety of the game must be played knowing that you could be killed by a newbie with a lucky swing of a hatchet. You remain vulnerable at all times. Even a lucky shot at you with a 9mm could break your leg, leave you sprawled on the floor, trying to bandage yourself or keep from going unconscious while your underpowered opponent kills you with whatever strikes his fancy. Similarly, because the world is persistent, you can be shot by a sniper at any moment. At which point you simply die, and have to start over. This might leave you bitter.
Because trust is an element of the game, you can also feel guilty or ashamed of your actions, because you are affecting real people somewhere in the world.
If you run into another survivor, and yell at him not to point his gun at you and that you're friendly, and he does not respond, you start to wonder if he's chatting on a side channel with some friends who are going to come up behind you, or if he's sizing you up and deciding if you have any good kit worth taking. You might shoot first, feeling threatened, and discover that his mic wasn't working, or he doesn't speak English, and you just killed him even though he needed help and wanted to team up. Alternatively, you could approach everyone with a big smile, completely unarmed, and offer your assistance, only to be shot in the back over and over and over and over again. Who could fault you for becoming bitter, and shooting others on sight, even if they were claiming to be friendly (but can you trust them?). Maybe you've got some good kit, and you don't think it's worth the risk to team up or help others. There are so many possibilities for user interaction that it's impossible to know what is going to happen next.
If you have any interest in this kind of game, do a youtube search for DayZ and see how people are playing now.
I don't own DayZ, and probably won't buy it until the standalone version comes out. Unfortunately, because a mod is essentially a hack, there are many security issues which cannot be addressed due to lack of access to the ArmA engine. So there are serious problems in the game with cheaters. Many of these cheats and game bugs have been fixed by third party apps run on individual servers (servers which do not sync with the "world" servers), so there is still the possibility of enjoying the game in its pre-alpha state (which over 1 million people do), but Rocket is working on fixing these issues in the Standalone version of the game to be released this year.
Good overview video.
More advanced play through video.
Advanced team tactical play video.