If XCOM reminded us of the value of loss in 2012, DayZ was a valuable lesson in hardship. The Arma 2 mod was one of the least-forgiving and most intimidating games of the year. It was a shooter that you entered without a gun. Arma's control scheme made actions such as inventory management a hassle; its 225km2 landscape asked you to run mini-marathons to get around, often without a map. Permadeath and persistency lent consequence to every action. And in its alpha state, DayZ was buggy and vulnerable to hackers.

1.3 million people played it.

DayZ is heartening; it reinforces what players are willing to put up with in exchange for novel, self-authored experiences. It's a rare shooter that gives banal tasks such as searching for water or riding a bicycle as much meaning as firing a gun.

Among bandit pursuits, lucky loot runs, mourning the death of friends, and castle raids, one of my unforgettable moments is when my friends and I accidentally orchestrated our own sniping mission. We'd arrived outside Chernarus' Northwest Airfield: treacherously naked terrain with the potential for military loot.

With empty backpacks, two teammates moved in. If they fired a shot, they'd ring a dinner bell for the undead. But 500 meters away, atop a hill, my sniper rifle was out of earshot. This was an escort mission: their lives were my responsibility, and Arma 2's ballistics meant I had to lead targets on two axes, manually dial-in my scope, and read my map to estimate ranges. It was a pure and exhilarating shooting experience, but more importantly, an expression of our teamwork. Moments like this in DayZ arise simply as a result of the mechanics, vulnerability, and players' natural storytelling ability. By being so hands-off with us, DayZ gives us ownership over every moment.

Read More: DayZ Photo Diary .

Runners Up: Black Mesa Source, Sith Lords Remastered.