I got really stuck into this for the first few hours, but I realised partway through that it wasn't really going anywhere; there's no story - it's just a survival sandbox. I thought it was a main campaign, but for some reason, that made me lose interest pretty quickly even though exploring the world and surviving is pretty interesting. I guess in that sense it's fairly unique (at least I've not played a procedural zombie survival game before) but I was really hoping for some kind of story progression rather than just finish people's missions, then infinitely move to another map.