Zombie Apocalypse. Enough said!!
Fantastic, intense, adrenaline fueled action. This game is a shooter. Pure and simple. Get from A to B without dying, and kill as many of the ravenous hord as possible.
The thing that sets this apart is the AI "director" It keeps every playthrough different and matches the challenge to your abilities as you play.
Playing the game by yourself is surprisingly fun. Your AI controlled teamates do a good job of taking out the attacking zombies, shouting out when they find weapons and ammo, and more importantly, coming to your resue when you most need it.
But this game is amazing when played with friends. Co-Op play, either split screen or online, ups the challenge/difficulty and brings a more tactical feel to the action. As you really do have to work together to survive through to the next safe house. Lone-wolfing it will get you dead fast and make it more difficult for the team as a whole. Nothing brings friends together like gunning down a marauding pack of ravenous zombies.