I voted that I don't like any of it. I think it should be possible to actively work towards goals, instead of relying on luck. I also think that work should be specific, instead of just having the player "level up".
Quest are a good way to unlock important recipes, like the workstations, steel- and cement-recipes, possibly vehicles (they could be rare and you get one as a reward for a difficult quest).
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Where it makes sense, recipes can be unlocked by increasing the skill. For example, start with a wooden club and the more zombies you kill with clubs, the more club-recipes you unlock. Same with armor, unlock recipes for better armor by killing zombies in close combat.
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