Your goal is easy and difficult at the same time because you'll have to survive. That means you'll have to sleep, eat, not to panic, steal things, fight against zombies, help other survivors, etc.
Graphics, viewed from a top-down view and retro look give that sense of unease you'll need to play this good game. In addition, you'll only view what the character would really see and the rest of the map will remain in darkness, so you won't view what's behind you.
Project Zomboid is a funny game with stunning mechanics and lots of hours of fun.