I made it! Really good puzzle design and it follows the theme. The first time I spawned I dropped through the floor. Reloading fixed it. I usually try to set my player spawn floor to -5 to avoid this as the engine likes to place you at 0 on the Z. This will cause the floor to "push" the player up and not fall through. I also got stuck in the elevator/rock room because I went in without picking up the gun so I had no way to knock the rock off the lowered elevator. You could just add another gun with the hidden rock in case players do that. Otherwise, very well designed.
I really liked the load checkpoint menu with the images.