It's good to see another GZDoom user in this gamejam!
This was absolutely incredible. The puzzles immediately clicked and were easy to figure out, and then the game immediately threw some twists at you for it. If this was expanded on and fleshed out, I could very easily see this being something lauded.
A few problems that I had:
One, the lack of music really made things feel kind of barren. But as soon as I put on some Necros (Point of Departure for the main levels, Energia for Machinehead), it felt perfectly right.
Two, the autoaim being set at 35 by default really really hurts the level where you have to fire over the fence. I had to disable autoaim, and for folks not familiar with GZDoom that could probably trip them up.
Three, the final level made it slightly difficult to figure out what to do at first. First time I went through it, I tripped and fell on the floor and there wasn't really a way back up and I wasn't being hurt. I ended up needing to ~kill and then restarting the level. As it stands, you might want to either make that a kill sector or to put a teleporter leading to the start.
Aside from those three problems, though, this is easily one of the best games I've played in this gamejam. I would love to see more, if feasible!