I started playing Lifeline, it's fun but less sandboxy than the original game (and obviously Breakdown). The increased zombies are nice but it's not done very well. Early today I stopped my truck in an area with no zombies around to get some camp package thing, I run over ten feet and get it and turn around and there is a juggernaut literally standing on top of my truck. The game pushes the idea that there are a ton of zombies in the city but the hard 'danger zone' borders are so hamfisted it's silly. Plus the map is deceptively small. Unless it unlocks later I was able to pretty much explore everything in the first few missions.
I haven't beaten it yet so I don't know how it ends, but I think I'd like it more if the game centered around there being a finite but massively dense number of zombies inside the city and you were a leftover military force tasked with cleaning up the city and making it safe or something.