Physics graduate here, asking what something "looks like" when you aren't looking at it doesn't really make sense because what something looks like is basically saying "what do I see when I look at it". If you look in the mirror and see the table and then turn 180 facing away the mirror is still reflecting the image of the table at the back of your head it just isn't hitting your eyeballs. Try standing with your back to a mirror with a torch or a laser pointer aimed at the mirror, you should see the light shining on the wall in front of you if it isn't hitting your back. Nothing about the mirror changes because you aren't observing it. There is an important concept in quantum mechanics where observations change the state of the thing that's observed but there is no need to think about that in this case.
Ok not ready to write a full response to this right now but I will say this, I guess I'm the first person you have encountered that wasn't underwhelmed by the ending. It certainly wasn't what I was expecting when I started but coming from the Campo Santo guys I knew it was going to be more personal and introspective rather than some earth shattering revelation about the nature of the forest. I really enjoyed the interplay between the characters and how the game dealt with Henry's "escape" from his life. As for reviewing the game I think the moment to moment exploration, the surprise, paranoia and dialogue matters as much as the ending and I really enjoyed my time with the game before it was over. I might write more when I have some time but in short I disagree with this.
"entire worth of a game's experience, and whether or not you will enjoy it, depends entirely on the last ten minutes of gameplay? and to comment on that 10 minutes in any way is to ruin the entire game for the player."
Edit: I also didn't really get a supernatural vibe from any of the preview stuff, your reaction reminds me of Gone Home where at first everyone thought there were going to be ghosts and it turned out to be something completely different.
The Idiot by Fyodor Dostoevsky. It's a long read but I certainly felt pretty shitty by the end. For something a bit shorter Where the Red Ferns Grow or Of Mice and Men ought to give you what you're after.
The Idiot is one of my time favourite books. Crime and Punishment is also pretty devastating if you haven't read it.
Ps: God that red line under favourite is making me freak out