7 days to die
Look, it's far from a perfect game. I and every other fan will tell you that. It's an FPS game that's basically mine craft with "realistic" graphics, and a goal: survive the zombie horde
It just hits a lot of points for me. There's creative building, but with much more purpose than in mine craft. Every 7 day, a massive horde of zombies tries to wreck your shit, so you must build a base to withstand that
There's a lot of knowledge of zombie behavior and design principles that go into bases that can survive modded hordes (Darkness Falls as an example). There are bases that force zombies to crouch for easy headshots, bases that line up zombies in single file as they run at you, bases that are just a fortified bunker you can shoot out of. You can set up multiple parts of the base so that you can direct the flow of zombies to where you want. There's an array of traps you can deploy, and different wiring elements can deploy the same teap in multiple ways
I'm on a time crunch. I'm not exploring the world just to look around, I'm not building a base because it's cool, I'm doing it so the zombie horde doesn't tear my head off. Which I like, I like having extrinsic goals and deadlines
Throw it all together, and there's really nothing like it
Mods are your friend, man.
Play Darkness Falls, Undead Legacy, or Rebirth
I prefer Darkness Falls because it brings back many gameplay mechanics from the early alphas
Undead Legacy and Rebirth aren't available for alpha 21, but you can rollback to alpha 20.6 and play them just fine