Super impressed with the pillar puzzle Michael, it really made me think for a bit. The design document is great as well, it really helps understanding your process.
I was born in the late 80's so I had my share of Dooms, Quakes, Heretics and Hexens.
From my perspective, and this is just an opinion, I feel too slow moving around the level, it takes too much time. Maybe if there was the option to run at the cost of stamina, that could help. I have the same issue with combat, it's slow and unresponsive; when I read Duskfall's description, I expected something fast-paced and chaotic. Id and Raven's games were crazy fast, that was the fun of it.
The music needs some love. You have invested +200 hours and money in a good looking game, don't use music from a soundpack, get someone to make it sound as it looks!
Are there any secret rooms? that'd be cool!
I hope to see more from it in the future.
Cheers,
Ismael