I just got Arma II yesterday for the DayZ mod on Saturday.
For anyone interested there are a bunch of youtube videos but here's basically what it is:
It's a zombie survival multiplayer game, most servers have 50 players. Your character is consistent. If you die you lose everything you have and start back at the newbie starting spot. Its very much pvp, pve, etc. You can trust no one.
You start off with a ****ty handgun, a few magazines, a small bag, a can of food, some flares, and that's about it (maybe a few other small things).
You need to find better guns, a map, compass, ammo, food, water etc to survive. The zombies can hear and see, so you need to move really slowly around them or you risk drawing their attention and wasting all your ammo. As a result it's kind of a slowish game with very intense moments interspersed. Lots of running, though, from town to town - huge in game map, would probably take 4 hours to get from one end to the other, maybe longer IDK.
Really great idea, lots of flaws in it right now but there's an open alpha so if you can handle the STEEP learning curve it might be fun for you. I'm not quite decided on how I feel about the game yet.
Very demanding of computer power, graphics aren't great, lots of loading into the game type issues, long load times, counter intuitive interface, but they are patching it basically every few days with fixes and improving it.
You'd need to buy ARMA 2 and Operation Arrowhead, and then the DayZ Mod is a free download.
I'll try to answer any questions but I'm basically a giant noob. I have managed to stay alive for about 2 days at this point though, average life expectancy is 27 minutes (lol).