Thanks for playing out game. Most of the assets were done by Dan (our artist) like the walls, floors, furniture, lifts, etc. were hand made by him. The Zombie was from the Asset Store and so were the guns and weapon/pickup effects. Here's his Sketchfab page:
The small tiles are a good catch. They're not the traditional Dungeon Crawler size but we felt they made the maps feel more claustrophobic, which is what we were after. The mini-map was a last minute addition and it's dynamically generated from the Tiled map that you load in at runtime so we were pleased with it.
Sorry about the (programmer) humor, We were trying to capture some of the Duke-Nukem humor from the 90s and give you a distinct memory in the first level to take away with you. The headbanging zombie at the start was Dan's idea but part of the humor. Did you see the Pause screen and the Level Failed screen? (again programmer humor.. sorry).