Good stuff! This is inventive and is a great proof of concept for several FPS gameplay mechanics. I liked the directional lighting effects and their multipurpose use to signal enemy location and flash when the gun was discharged. The glow-in-the dark feet are a nice little directional prompt for where to go too. There's a nice intersection between 2D billboarded sprites in 3D spaces and the opening cinematic was a great example of how to animate these to create illusions of depth and motion. I also wasn't expecting there to be a few perfectly functional physics puzzles which worked very well.
Can I also say that I loved the music? That 90s breakbeat sound is really enjoyable. I am also a fellow Reaper composer! It reminds me of playing Straftat which has tracks like this. It's great to add in layers beyond breakbeat loops, so the strings and guitar chords added a bit of texture that gave the track much more atmosphere. Really cool to see hand-drawn art and personally I found the dust bunnies kind of cute, in their own way.
For feedback generally - It's a little thing, but make sure the browser has exclusive control of the cursor so it isn't duplicated over the screen! For general ideas, part of FPS design is finding flow in the level design and working the shrunk-down concept into the setting and objects that inhabit it. With more development time, it would be cool to see how the spaces themselves could have a little more character and integrate the puzzle design into the level design more. Sort of a mise en scene, giving objects and elements a purpose for why they are there. That can help make levels feel like spaces to explore.
Thanks for checking out SYMMACHUS and I hope you had a fun time making Lint Breaker for the jam!