I did a quick search and I'm surprised this hasn't been mentioned in the forums yet o.0
http://www.dayzmod.com/ - The homepage with forums and downloads. I suggest going here and looking through the newbie section.
For any of you with ArmA 2 combined ops (original game and expansion), there's a mod I just discovered the other day and it's FUCKING AMAZING.
It's in alpha, so a bit buggy, but the amount of immersion I've had in the game is so far unparalleled by anything I've ever played (And I'm not even exaggerating o.0 )
The servers run with about 40-50 people on the map, Chernarus, which is 225km squared. It has a real-time day/night cycle (going off server's clock) and is free-for-all pvp. Your character is saved on a main server so if you swap servers, you will log in with all your stuff and in the spot you were at in the last server. Oh yeah, there are vehicles too, but those aren't as fleshed out as they should be since they're new.
The basics:
You start out as a survivor, tossed randomly into the world with nothing but a water bottle, a couple of food cans, some meds and a shitty pistol called the Makarov. From there, you're on your own. Your only goal is survival.
To find guns and food, you've got to scavenge around in houses and barns, or if you feel like being a douche, turn to a life of banditry and start shooting newbies.
Depending on where you go, you can often run into survivors, usually hearing them before you see them. These are the most tense moments in the game. Many a time I've spent 20 or so minutes tailing someone trying to figure out if they're friendly or a PKer, other times we've bumped into each other and had a tense mexican standoff where we both slowly back up, with guns raised, yelling at each other to "stop fucking moving!"
The big towns have better loot than the smaller ones, but you're MUCH more likely to find action with other players there. Bandits often go to the major coastal cities (Cherno and Elektro or something like that) in search of prey, which brings in the bandit hunters, trying to gain back morality points.
Basics of the morality:
When you start in the game, you have 2500 humanity. Killing a civilian will cause it to go down, killing zombies and bandits raise it back up. It can also tick up over time.
When you dip below 0 humanity, you get a special bandit skin (It's sorta desert camo looking) that lets people know to either kill you on sight, or run like a bitch. You're stuck with the skin until you get above 2000 humanity again.
It can be really hard to crawl back up if you go around killing people, but they often drop the best loot. Just be careful not to dip low, or get a reputation as a PKer or alot of people will try hunt you down.
The Zombies:
So the zombies are probably the buggiest part of the game at the moment (alpha is alpha) because they have really jerky animations and tend to phase through walls and stuff.
You can't outrun them, they're damn fast. They take 3 shots to kill with the makarov and a single zombie can knock you out in an instant and kill you if you're not careful. At the moment, they tend to spawn as you come into towns, so sometimes you can clear a place, come back in a few minutes and it has a zombie in it again.
You have 2 stealth icons in the top right. One is an eye. This shows how visible you are to the zombies. Standing in shadows, crouching or going prone limit your visibility. The other one is an ear. Obviously, that shows how noisy you're being.
You can generally crouch walk close at night without alerting them, which is good. They can REALLY fuck your day up. I got a bunch of good items one life and then a couple of zombies tore me to shreds and I lost it all
Vehicles:
So very infrequently, you'll come across a broken down vehicle. Some I've seen so far include a dirt bike, ATV, pickup truck and a Huey gunship.
When you DO find a vehicle, they're almost always broken. You need to go hunting around to find the parts it needs before you can get it up and running, plus it also needs petrol.
Honestly, I havn't touched this part of it yet, but I have seen guys burning about on a bike and popping wheelies, being chased by about 20 zombies. I lol'd.
Dying:
This game is 100% hardcore. You die, you restart a new character with only the starter gear. Your old body will stay around for a while and be completely lootable (you'll hear flies buzzing around bodies of dead players). To start afresh, you have to hit the abort button and disconnect back to the lobby, count to 10 or so, then rejoin.
Final advice:
My trust reaches as far as the end of my gun barrel and so should yours. You can meet people in game who are nice, but you'll quickly learn that sometimes they act nice just to shoot you in the back later.
The official trailer - think it's old though couldn't find a newer one.
That's the video-series that got me hooked.