Play before reading if you don't want anything spoiled or ruined.
I am really bad at writing so I hope this all makes sense.
The goal for Demons was to make a serious game with emotional impact, but we wanted to make sure the game was still fun to play. Sure we could have made a walking simulator with fancy graphics and a strong narrative, but we wanted to see if we could deliver a high action experience that conveys it's themes through play.
So we designed the light system in our game. Light is EVERYTHING. Your health, your ammo and a timer. It keeps you on the move, always searching for a point to refill it. It keeps you on your toes. It is stressful and that's a good thing. It causes the player to feel what our protagonist is feeling, which adds agency to the experience.
We also designed the gameplay to contrast the light system. It makes the player want to go fast and shoot frantically, but that is far from the best approach. It turns expectations on their head, causing the player to take a slow, careful approach as opposed to a guns blazing one.
Another mechanic we experimented with was variable difficulty based on player choice. It is presented as a questionnaire at the start of the game. What you answer there directly influences how hard the game is, and how long you need to survive to win. We think it's an interesting approach to difficulty, especially since we never explicitly tell the player that their choices will matter. A hidden mechanic that matters a lot, yet remains hardly noticeable to the player and doesn't break their immersion.
When all is said and done, I think the game turned out very good. It has some cool design ideas that I'd like to explore further in a project with a longer deadline in the future.