After our astonishing interview with The War Z's executive producer yesterday, it comes as no real surprise that Valve has stepped up and pulled The War Z from sale on Steam until Hammerpoint sorts out its issues. Customers who already bought it via Steam can keep it if they want; those who don't can get a full refund from Steam support. Valve also admits it made a mistake in releasing The War Z in the first place. Valve's full statement below:

Valve: From time to time a mistake can be made and one was made by prematurely issuing a copy of War Z for sale via Steam. We apologize for this and have temporary removed the sale offering of the title until we have time to work with the developer and have confidence in a new build. Those who purchased the game and wish to continue playing it via Steam may do so. Those who purchased the title via Steam and are unhappy with what they received may seek a refund by creating a ticket at our support site here: https://support.steampowered.com/newticket.php

Again, we apologize any inconvenience.
That's about all I can ask from Valve in a situation like this, other than some kind of assurance that new policies have been put in place to prevent it from happening again. I'll follow up on that.