This was a really well made and a very fun horror game! The story, voice acting and the simple progression was really well done and straight forward. The stuff in between were well placed so that it didn't feel like there was a long gap between the interesting or scary parts (except the bathroom part, though the Easter egg was nice!)
You absolutely nailed the sounds! Whenever there was a sound, it was genuinely scary and it added to the atmosphere so well and made everything seem that much scarier! And the small map really helped focus in on the main parts of the game and elevate those scares as well.
One 'glitch' I found was that you could get stuck in the hung body room, not sure if that was just me doing something dumb but thought I might as well write it here. Another I saw was that the monster duplicated itself at the vent area if it catches the player; I saw the monster standing behind its jumpscare body.
Other than that, it was a great, great game! Unexpected main menu and faced paced with plenty of Easter eggs and good scares. You've done a great job and have improved a lot since The Book!