I loved the concept! It's a really fun scavenger hunt that involves using the mirror's reflection to look for stuff that doesn't appear to the naked eye.
I got two spine chilling moments and that's great! Good atmosphere!
The only bad thing I encountered is the second door didn't open during my first playthrough and I spent a lot of time looking for a clue that didn't exist. Also, after the final clue, I was transported inside the fireplace haha.
Good stuff!