Things that would have made Amnesia scarier

[Bottle Dog]

More enemies like others had said

When sanity is very low: rooms will start to change in dramatic ways. Like You exit a room only to find that you are entering the same room. walk down a long hallway only to see that you have only walked a few feet from where you were. lanturn becomes a severed head. see bright blue light coming out of some doors. Hear monsters right next to you even if there isn't any.

In the study room have a dead mutilated dog come crashing in the window from the outside. (Lol watchmen)

Hear knocking sounds on doors with low sanity

In the sewers have a giant wall of water come rushing at the player while he's walking to a small hall/walkway when he has very low sanity. but when the wave is about to hit the player make it disappear.

Have a fire start and spread in a random area. when you touch it it disappears

Have something giant crawl out of one of those doorways that have those boulders and cobwebs things that breathe. But do it late in the game when the player thinks that they are nothing.

See giant spiders crawling on the floor like the one in penumbra when sanity is low. like before, touch them and they disappear.

In a silent dark area have a guy on fire run past a doorway while screaming in pain.

When sanity is very low see a pedastool down a hallway with an orb in it glowing blue. as the player moves closer everything becomes darker and quieter. when you touch it everything goes back to normal