Hello, I played Amnesia some months ago and I just registered on this forum, although I lurked for a while.
Don't take me wrong, I absolutely love your games Frictional, they're the best and only horror games that scared me.
I will add my suggestions to the problem I am talking about if I have one.
Right, I'll start with it now.
1. Music
The music is great, but a special danger track starting when the monster spawns and stopping when it despawns can have some negative consequences on the game.
I'd personally make it so the danger-music is not stopped until you reach the point where the monster despawned.
2. Replayability
None of them are random or based on amount of time spent in a certain area. There are conditional spawns depending on sanity (does that work for health too?), but there's not enough of them to add replayability-value to the game. During the first playthrough I noticed the dangermusic playing, which also killed a bit of the replayability value.
What I'd suggest here is a timer, say someone spends a lot of time solving a puzzle, the person won't experience anything different at second playthrough when s/he solves it fast. Another good idea is to make some monster spawns depend upon the order you completed different mementos. You could also randomize some spawns, where you trigger the randomization when doing something. This could be a _Bool value (assuming you use C or ANSI based language).
Spawns in one puzzle-area or so would not hurt.
3. Puzzles
Some puzzles are too simple. I know this is not a puzzle game, but they do add a lot to the gameplay. I have no suggestions on this one sadly.
4. Monster spawn sounds
While they do add a horrifying chill down my back, I believe they should not always play spawnsound when they do spawn. This would make the game scarier, as you can walk down a dark hallway and you have no idea if there's a monster around or not unless you hear it walking or making sounds. When they don't make a spawnsound the danger-music should not play until you know the monster is around.
5. Monster AI
I know an AI is not easy to program, but some countermeasure for sitting at statues or other things. Personally I never did this, but I saw people who did.
I would advise against making "invisible walls" around statues and such, as it would break the immersion a bit, and it should still be possible to climb on to them. The monster should be able to counter it some way, for example not leaving until you go down and hide.
6. Patrols
When a monster has spawned and it sees you it should patrol the nearby area where it last saw you. If it bashes down a door it should enter and check the room, instead of entering and turning immediatly, without checking the room.
7. Sound effects
They're great, I admit they made the game horrifying, but there seems to be a lack of them later in the game. In the beginning you can hear footsteps etc.
I do believe these footsteps and such would make the game even scarier for example in the storage.
8. Small events
I don't see doors blasting open by wind in the later game, neither do I see many torches going out due to wind etc.
I believe these could still be useful in the lategame.
I only intended this post as constructive criticism, and I hope you make the next game perfect, Amnesia was not far from!
EDIT: What programming language do you guys use anyways?