The game is very well made, I enjoyed a lot playing it! But the checkpoint before the monster chases you for the first time is very poorly placed. It takes ages to get back to that room and activate the power again. The player already knows that there's nothing in the hallway before that, so it's just a boring walk.
Also, there's a bug where it sometimes wouldn't let me go up the stairs to where the red button is.
But other than that, very nice game :)
edit: the checkpoint is fixed in the latest update