I enjoyed this game. The doom/duke nukem vibes felt good and the atmosphere was thick with the threat of the zombies making you feel uneasy and constantly on edge.
I have to say I got lost though.. I found like four different codes and when I found the one that was accepted I ran around everywhere looking for what changed to no avail. I'm not sure if it was a bug or just me, haha. I also feel like the enemy spawns added a lot of tension but maybe to the impediment to the exploration. Perhaps linking it to something like the player's progress would've felt better?
It was fun regardless. Nice submission!