Atmospheric and creepy in equal measure. I loved some of the visual effects, like the rotating shadows in the dome room, or the corridor of rotating squares. The optical illusions they caused were very trippy!
I did get stuck for quite a while on combination lock doors puzzle, but fortunately stumbled upon the method for solving it.
Bug-wise, there were a couple of things to note:
- A couple of brief audio glitches while I played. Not sure if it was the game or my PC though, and no obvious triggers, so seemed random.
- There were a couple of places where the player model gets caught on geometry. 
Going up these ramps, some of the 'discs' stop the ascent and so you have to jump over the lip.
Ascending back up these stairs towards the end, I got stuck on the penultimate step and so and to jump to clear it. I can't remember if that happened every time as I went up and down several times exploring.
I did record a video of my play through and could post that to YouTube if you want to see it.
Otherwise, I enjoyed my time running around the monument, and was kinda disappointed when it ended so soon. 😁