I have to say, although I enjoyed what I've played, I feel like I sort of ruined this game for myself, here's why (not sure if I need spoiler tags in this thread, but everyone else seems to be doing it):
I found the secret passage for the key to the attic too quickly, upon entering the house, then went into the attic as soon as I found it. Now I have (at least) two locked doors to explore with no sense of mystery left, or really any sense of the ominous atmosphere I was enjoying.
Did this happen to anyone else?
Didn't even know that was possible. I feel like doing a speedrun of the game now. I guess this really just highlights the fact that you shouldn't play the game like Wolfenstein 3D...
BTW, there's actually a modifier that allows you to start the game with everything unlocked, so I guess they did intend for at least some people to play it like that...maybe.
I thought the game did a good job at teaching you that you don't need to pick up everything, or check every wall, I just learnt that lesson a little too late. I wasn't even trying to find secrets, it was a complete accident I found it. I don't know if anyone else found this (I'm not sure how you're supposed to find that particular passage later on), but I could imagine it being pretty cool finding out you'd been walking back and forth past the key for the whole game.