Its for xbox and pc (Maybe ps3? idk) It has 2 episodes currently, but i must say the second one caught me off guard. I wont spoil it but its amazing! you have to pay for new episodes, and its a story like game, (More based on decisions then action)
Its not entirely sandbox. But its based upon your in a zombie outbreak, and you need to make choices to help your group live on, but bad things happen, which make your choices hard to make.
Each ep costs $4.99 but u can purchase a season pass type thing that'll get you all eps cheaper. Really good game I must say. The writing is top notch stuff