Continuity mistake: During the events of 'City of Ashes', you can sleep a little in the survivors' headquarters on a designated bed, that triggers a short, surreal nightmare-sequence. Now, if you use your guns or explosives within the dream, the ammo loss will be present even after your character wakes up - it makes no sense.
Revealing mistake: If you get a slow motion bullet cam shot on a zombie wearing a helmet or hat, and it's a head shot, you can see the hat fly off when the bullet hits, but often you will see the layers of the hat pass through the zombie's head with no collision.
Trivia: Labyrinth of Death: After the first safe room, you have to go and hit the control to manually open a large door. It takes the door a few seconds to finally start opening. There is a horde of zombies on the other side waiting. Once it opens, if you are zoomed in with binoculars, your sniper scope, or happen to be right next to the door, you can see the zombie in the middle at the front is standing there saluting for a moment, and then snaps out of it and starts coming after the players with the rest of the horde.