This game is close to being great, but falls short on the long game. The first thing id suggest is bigger maps. The whole region, including the outside areas that you just send raids too should be fully playable, raiding the same as the center and the ability to build. There should be buildings that are unique builders. Like the arms factory, you should have to discover, claim and secure it, to use it. If your smart its quite easy to direct the infected into kill boxes and control the flow if you build well, by having zones outside the main zone it would make it much more challenging and give stronger objectives. The bigger the map and the more complex it is to reclaim it the better the game will be....

Oh and much much bigger hordes. Even very hard settings with max infected isnt a challenge at all on a decent map with a good base and smart horde management. (use cars to herd the hordes, break them up so your towers dont get overwhelmed)

Also, longer days and nights. It takes an hour to drive somewhere it should take 15 minutes. Also this would allow for more tactical play, especially with bigger maps