Look it up on youtube for other people's perspectives, and I have no doubt we all know what it is by now, but I'll sum it up.
DayZ is a large multiplayer zombie modification made on Arma 2 w/ Operation Arrowhead. (you can use Arma 2 Free in Arma 2's place if you want, just lower textures) made specifically for the Chernarus (whatever that means) which is a big ass fucking map literally spanning 225 kilometers squared (trust me, it's really that big, in the literal sense), where players must scavenge for supplies gear and weapons while dealing with zombies and enemy players alike. ArmA 2 itself is a military combat simulator, so basically, head shots = instant death with fuckin anything, and a shot to the leg forces you to get down on all fours to keep moving (broken leg), bleeding, etc. There's also ghillie suits. And they are straight up jack pots, assuming you've gotten a decent weapon already. Since most of the map is grass and forest, just hide in the grass, and pop whoever happens to run by.
Going Solo: The only real way to play solo is to either be extremely sneaky or extremely fast. So you're either crawling or sprinting 24/7, trying to avoid players until you get a decent weapon and then either camp a spot or just go berzerk until you die. (Don't bother trying to do anything else, you'll get hunted down even in the middle of fucking no where on a population of 10 server and get shot one way or another)
Groups: It's nearly impossible to organize since most people spawn away from each other, so you literally must memorize the map to even have a chance. From there though, it becomes a lot more interesting, being able to, as a collective group, look every where and keep an eye on each other's backs, can systematically destroy everything in their path, granted dick headed random snipers (people LOOOOOVE doin dat) will always pop one of you eventually, it's a lot more fun and interesting. Practically becomes a sort of town control if you have enough people, locking down a small town or area, waiting for stuff to spawn in say, a military base for good weapons and ammo.
The game itself takes a lot to run, however. It's more of a CPU hog than most games, most people recommending ridiculous over kill like an i7 straight up. My Intel Core Duo E8400 at 3.0 GHz Does perfectly, TBH only ever going over half of it's power.
GPU on the other hand, the recommended is a GTX 260. A geForce 8400GS won't cut it, well, not very well. Currently running the game at 800x600 everything lowest on arma free no less, still, in cities I get 10-15 FPS on average, elsewhere it's rather smooth. But looks like shit. Almost blurry. Not to mention I have almost 3 gigabytes of memory for the card. But thankfully I got the version with a heat sink, instead of a shitty 2 inch fan. so I could over clock it and get much better results, but I'm gonna wait to do that when I know I've got a decent replacement on hand incase something were to go awry.
So there's that. It's a pretty good game but IMO I don't like how it's pretty much an open world Death Match server much less a zombie survival game. Everyone shoots everyone with very few exceptions.