State of Decay is a zombie survival game that just came out for the 360 arcade. Unlike Left 4 Dead or Dead Rising, fighting zombies isn't the main objective, survival is. Like to find food for your group, you have to sneak around herds of zombies, creep into the Quicky Mart, and search through the shelves for Twinkies. (Twinkies are an item, BTW)
The game is fun as hell, full of moments where my friends and I squeal like little girls and yell, 'Run to the car, RUN TO THE CAR!' Gunfire attracts the undead, so melee weapons are usually the safe bet. Lots of references to zombie movies and games and comics. See:
It's a bit buggy, but an update is coming soon to fix some problems. Multiplier too. This game screams 'Co-op' and yet, none.
Think Walking Dead. Small country town overrun with the dead. Big cities are dangerous; wide fields of wheat are lonely, but safe.