What is Projekt Z?

Projekt Z is a free-to-play first-person shooter set in a WW2 Zombie scenario on a secret German island. The game focuses around the "Projekt Z", a project run by the Nazis to turn Zombies, which have been discovered on the island earlier, into weapons to turn the war around in Nazi Germany's favor. On the Island, you will discover various secret Nazi projects related and unrelated to "Projekt Z".

The core gameplay of Projekt Z is explained easily:

You have the HUB, you can craft weapons, ammo, and other consumables here. You will also be able to build things inside the hub (similar to Fallout 4's settlement building). From the hub, you start missions. Missions belong to a story arch and can influence each other, depending on the order in which you do them. An example: a mission where you clear the island's sewer system will lead to different zombie types appearing in other missions that otherwise were trapped in the sewer system.
Story arcs have a beginning and an end and shall not be stretched indefinitely. After all, the best stories are those that were planned with a definitive end in mind.
During missions, you can find items, building materials (for the hub) and recruit personal for your hub.
Missions can be repeated for gathering more materials/loot.