Version 1.1

Thank you everyone for the feedback. This update is mostly small modifications of the existing code, but I am excited by the overall impact.

First of all, the game is now brighter! After hearing the feedback about the game being too dark, I tested it out on different monitors and adjusted the amount I was darkening the scene. Hopefully, the new result makes things a bit more playable while still maintaining the original atmosphere.
If I were to continue with this project, the goal would be that the brightness would be a configurable value available to the player, but for now, I hope this is a more appropriate base level. I also hope to experiment with some different dynamic lighting solutions to further bring life to the environment in the future.

Secondly, you can now aim behind you! This was left out of the original implementation for three reasons:
1) I wanted to keep the players focused on moving forward in the scene. Since I had no mini-map and very few unique landmarks, I was worried that giving full camera control could distract the player from progressing through the level.

2) Early in development I was dealing with gimbal lock issues when rotating the camera. Limiting the rotation around the y-axis seemed to minimize the chances that players would encounter this. The issue had been resolved midway through development, but I had not removed the limitation.

3) I had not built an environment behind the spawn point. Allowing the player to turn around would highlight this fact.

When it was pointed out by multiple sources that you could enter an unwinnable game state if you run into a can while backtracking, I decided it was worth removing this restriction on the player's movement and trying to address the original concerns I had in a different way.
I still reset the player's orientation when entering/exiting the aiming mode (so as to keep their attention on progressing forward through the level), but when in aiming mode, you now have full freedom to aim behind you. Hopefully, this should make those last couple cans easier to spot.