I thought it was a fun concept! I just think it went on for a little too long and with almost no variation. I also think you could´ve added a little bit more story with the notes that appear in the hallway.
To change up the repetition a little bit maybe you could add obstacles that make it difficult to complete the task that it gives you, for example, maybe when it tells you to "look right" the game makes you turn left forcefully and you have to fight against it to keep looking right. I would also enjoy more sound design, especially when it tells you not to move, maybe you could make it that the shadow comes near you and walks around.
But overall, I liked it!