I don't like the idea of thorough exploration and backtracking unless it's for a task. As others have stated, a major factor of horror is the concept that the player cannot control where they can go all the time.
Tight, constricting hallways and a select amount of rooms are almost perfect to create the horror scenario. Allowing the player to roam freely collapses the dread they once felt at the beginning. I'm not saying disregard exploration entirely, but it should be given in moderation. I love to get the feel of the environment and back story for any game, but and excessive amount destroys what the game's goal is, you know? A game like this needs to make the player feel helpless.
Hmm... A common suggestion, I'm sure: Obvious monster triggers are a turn-off. They're scary, but after a while it's like, "kk, I won't grab Mission Object XYZ until I build a fort out of a crates. I'll be ready!" Randomize monsters a bit. It spices up the fear. <3 I like the idea of accidentally walking into a hallway which has a wandering/patrolling creature.
And maybe more monster types? I'm sure Alexander had female servants, too.
Sometimes I wondered if it was just 1-2 monsters through the whole game following me (1 gatherer, and the 1 brute). It'd be more plausible to NOT see copy-paste monsters everywhere.
Yep.
Amnesia is awesome, though. No doubt about that. one of my favorite games ever, for realz.