eRe4s3r: TL;DR
Jump scares are not scary to me, but of course I have an reflex reaction to them. I actually find games utilizing them to be the "cheap" kind of horror. Only horror game so far that actually made me feel really really tense and anxious was Alien Isolation. And only until I understood the gameplay properly. It's funny but the longer you play Alien Isolation, the less scary it becomes, but in between all the tension it finds some GENIUNE creepy moments, like running away from robots (Which are very creepy...) into a vent and suddenly being face to face with the Alien. THAT made me avoid ventilation shafts nearly the entire game. And this happened very early (From what I hear, some people NEVER had that happen to them.. hah ;p)
But I will say this, headphones or proper 5.1 or better sound system are absolutely vital to actually feel the horror in horror games properly. Especially in Dead-Space the sound environment in certain sections... or when the Alien just randomly drops down a vent in front of you completely out of nowhere....
For a TL;DR is pretty long, if I dare say, longer than the not meant to be short answer? ._.