Such a simple main mechanic - having an action that requires player to focus on one place but keeping their attention to their back as well. Really keeps you on your toes.
The atmosphere: birds, creakings and various fake-outs make this work well.
At the very end I was celebrating so much that I missed whatever the heck happened when I hit the monolith and stared into the main menu in confusion, lol. The ending could be better :)