Things that would have made Amnesia scarier

[Kreekakon]

I mean, the first time i've played, i got killed by the grunt. After i saw him, i become more familiarized, so, the fear i felt before wasn't the same, because i already know him and he appeared a lot.

That's "after" you saw him. New monsters would share the same effect as that before being seen, and getting familiarized with.

For a game like Amnesia, I'd say its monster variety count is okay. Having too much can sometimes diminish the experience by having too many monsters to "know" when compared to having a sense of dread/attachment to fewer a variety of them.