Blasphemy! Say no more, purge these thoughts from your mind and re-watch it! ;-)
I'm just kidding. But I do think Alien is a masterpiece. Saw it last year in a theatre. It was the first time I had seen it, and I thought it was amazing.
Anyway, I'm not well caught up in my horror films. "Suspiria" is very, very scary. The original "Vanishing" (the Dutch version, not the American remake) isn't so terrifying as it is unsettling. It all seems so real, and the ending is just a knockout. It's not a twist, just one of the most mentally disturbing endings I've ever watched.