I'm a PC gamer, in an over age 30 clan and all. We do FPSs like the Battlefield series. But recently a MOD came out for Arma II called Day Z. It's a survival 3PS/FPS zombie Apocalypse experience. I call it an experience, because it's hardly a game. Arma II and it's OA expansion are available in stores and on Steam for $30. The MOD is free and has 1.1 M players. Nearly 5x what Arma II ever got!
This mod is in Alpha state and bugs are found and patches come out often. Also hack/scripters are prevalent.
Still, this is a sandbox gaming must if you have a decent PC and Video card. If you play consider joining my clan's server and Ventrillo. We are US Server 673 =HOG=. Our website is www.hogclangaming.com