Best sandbox zombie survival game.

(+)
Big, procedurally generated world.
Interesting survival/base defense mechanics.
Adjustable difficulty, lots of options to tweak.
Mod support.

(-)
Need more building variations. You will see a lot of the same things. Mods can alleviate that problem, though.
Need more zombie variations.
Some ridiculous zombies, and some buggy ones.
Need expanded options, like setting the zombies to never run at all, or removing some types of zombies. But, again, there's the mod support.
Still in alpha stage, so expect a lot of starting over due to save incompatibility.
Cruel RNG, but maybe that's just me.

Best sandbox zombie survival game. (+) Big, procedurally generated world. Interesting survival/base defense mechanics. Adjustable difficulty, lots of options to tweak. Mod support. (-) Need more building variations. You will see a lot of the same things. Mods can alleviate that problem, though. Need more zombie variations. Some ridiculous zombies, and some buggy ones. Need expanded options, like setting the zombies to never run at all, or removing some types of zombies. But, again, there's the mod support. Still in alpha stage, so expect a lot of starting over due to save incompatibility. Cruel RNG, but maybe that's just me.