I've never really thought of Pac-Man as a horror game. Innocently chomping away, dodging ghosts from a top-down view is pretty tame. But taken from a first-person view, where you simply don't know what's around the next corner, is a whole new horrifying ball game.
It's survival horror in an arena that looks like Tron crossed with a derelict space station, and you can play it for free right in your browser. There's something quite empowering about chasing down those pesky ghosts in first-person once you've munched a power-up.