Thanks, I'm glad you liked it! I like old fps games like the Build engine games and some odd ones I played here and there like Future Shock and Chasm and stuff like that.
If you're in the first area, you have two ways of proceeding. The main way is to shoot the spinning wheel thing, opposite of the main menu image. Or, the speedrun-y way is to jump on the bed, jump up to the top of the wall and you can get anywhere else you need to go--or anywhere else really, including the end section. I thought it was a funny thing to leave in.
The theme of decay is the ending (decay of humanity), the shotgun itself (decaying the environment by shooting through things), and the visual/downsampled audio. One time I tried to play an old FPS game and the textures didn't load at all, so what I saw was similar to this where everything was a single color. It was inspired by that partially, where a game I tried to play was decayed.