To be honest, not many games are genuinely scary. The ones that pull it off are exceptional.
Resident Evil on PS1. Never experienced jump scares before but when the zombie dog crashed through the window, proverbial bricks exited my person.
Alien Isolation for me is the most genuinely frightening game in recent memory as it didn't rely on jump scares and managed to conjure up a constant cycle of dread with punctuated moment of genuine terror. You actually had to hold your breath and not make a peep for god's sake.
So there is it - Alien Isolation.
