the MONSTER was never scary to me, but i always get the chills when the music starts playing, and when i don't see him its even worse. I don't know why people think that thing is so scary, or any of the monsters from amnesia

The monster itself doesn't look very frightening, if anything it looks a bit goofy and, albeit, a little unsettling.
That being said; the game's ambiance was enough to scare the ever living crap out of you. It doesn't matter if that thing was the sweetest, cutest little bunny in the world, I'd still be terrified of it simply because of how the whole game surrounding it was set up.
I still remember how horrified I was when the door started splintering apart for the first time because he was banging on it and a little note appeared at the top of my screen saying "you don't have any weapons, you have to hide."

True, i remember playing this custom story where the creator replaced the monster with a character from my lite pony (i dont know wich i am not into that :/) and it was more frightning that the original monster, especialy cause of the voice he gave it.

The chained, eyeless Fluttershy? (yellow one)

Even more scary. ._.

Yes

Fucking thank you. When I downloaded Amnesia, I was certain a game couldn't be that terrifying. So I did it at night, with headphones with the computer connected to the TV.
Fuck

I was even more scared when that high pitched noise happened and I heard his grunting but still couldn't see him, I even got hit by him and went on to flip shit.

Yeah, that noise is what we are talking about :3