Yah I remember the first Silent Hill was the first movie to ever scare me the way it did. It was the first time that I wasn't sure what to do, look at the screen or cover my eyes (seriously). I went back and forth, not wanting to miss it, but a bit too scared to look. It builds sucha strong creepy atmosphere, and tha air raid horn, I have always found that scary sounding even before the movie. The part I am referring to that freaked me out that way was the janitor coming out of the stall, I don't know why, just extremely creepy and weird atmosphere and the movie just thrusts you in. I loved it. I cannot wait for the second one!
But different things care different people, I find demons/monsters scary, but some find the more realistic films scary like Silenece of the Lambs. Yet slashers are my favourite I don't know why haha, maybe cause they were the first true horror films I had seen.