Until Dawn certainly wasn't scary as far as I'm concerned, as it was obviously very goofy and full of horror cliches (like most modern horror movies) - although I'm not saying that's a bad thing. It was actually quite a refreshing setting for a horror videogame, which have surprisingly rarely gone in to the 'group of annoying teens in a cabin in the woods' sub-genre in such accurate fashion.
What it was however, was tense. Because your choices did matter, and if someone died it was a direct result of those choices. So it was the tension and responsibility, rather than scare factor, that made the game stand out for me. The only issue was I couldn't care too much about the characters - and in a horror movie that's obviously by design. They are annoying self-centred teens so you don't mind so much when they get killed off in some gruesome manner. But in a videogame where your choices need to matter, it is more of an issue.
But in terms of horror, for me it's atmosphere rather than jump-scares that stands out for me, primarily because I get more immersed. And that's why I have to agree with other who cite games like Alien Isolation as being more 'scary'. But that's not to say Until Dawn didn't have lots of tension, because it did. It's also a vastly underrated game that didn't get the attention it deserved at release, but luckily many got to experience it when it was free with Plus.