I was certainly younger but I don't think I was any more impressionable than I am now, but you're right, the subtle approach can be very effective. I think NLD had less effect on you recently because you didn't see it in a theater. And you'd already seen it. I don't know. I admit I have not seen NLD recently. Maybe this means horror thrillers have a shelf life. But it got to me at the time way, way more than Signs did, not because I was young but because it was horrible, and Signs didn't horrify me, though Signs is in some ways an impressive movie, and hugely more professional than NLD. Blair Witch Project was pretty scary, even though you knew it was fake, and it cost nothing. So I don't think budget and maybe even directorial skill are important factors in making a movie scary. Not always, anyway. Hitchcock had tremendous directorial skill and his movies were scary too. There's no clearcut rule.

I'm just surprised people find Signs scary, because the alien menace is so poorly established in the movie. It's just roughly sketched in. In the worldwide terms. I know there are a lot of noises and stuff, but a global alien attack has to be established by more than a few TV and radio spots. I think Shyamalan was copying '50's style in that. I don't think he cared about the alien stuff. He was interested in Mel Gibson's character's re-conversion to faith.