This game makes a very good first impression on me, similar to maybe Lotus Turbo Challenge 2 back in the day or D/generation. Mostly the artwork looks good and works well with the music, though maybe it is fair to say that it doesn't always look as if polished to perfection like in a lot of A+++ commercial games but often you could call it close. The weird distance blur with the raytracing definitively gives it this unique retro experience, albeit looks somewhat grainy and sometimes off, but not in a bad way.
Back in the day this would have been quite a success. But by nowadays standards it is extremely basic in design, not enough to grab attention for long. For today's games to stand out, you need to introduce novelties (e.g. swarm-intelligent enemies), complexity (e.g. building, crafting, inventory, gear-modding, skill system or interactibles like NPCs, computer terminals, etc) and/or intriguing and immersive storyline (I only played the first level). Implementing this obviously takes work and without a modern game engine like Unity or Godot, the overhead to do everything from scratch without any tools becomes so huge, it is sort of impossible to get very far. So I understand on the one hand that this is out of the scope of this game and it is just a simple neat and unique looking FPS. On the other hand though, since the game is very nice from the visuals and sound, it makes such a good first impression. It is kind of a shame that it won't be much more than that.
The fact that it runs without a FPU on only 32KB RAM with no dependencies, well this is not meaningful at all to the player experience, unless it maybe concerns some ultra-niche audience. It is kind of like Amish people refusing to use power tools and modern medicine, it is sort of just besides the point of life / gaming to do this. I don't know what it meant to you, maybe it was more fun to code like that. But for the consumer it has no relevance, so I totally ignore that in my review. Also I briefly flew over some of what you wrote about free software, without reading through it. That's partially how I came up with the Amish people comparison. I think it is something to really think about when writing software. Because if you quit following the revolution, you just get outpaced and overtaken by what life and human existence / software is really all about. And before you know it, society starts looking at you like an endangered animal species in a zoo, that cannot really serve a useful function anymore in its once natural eco system because the way it functions is just too primitive and unevolved, but somehow still worth to keep in memory if looking down on it from above. Don't write software to become an oddball exhibit. Follow the revolution, use the Godot engine. There are downsides to everything, but staying on the overall upside must be top priority.