Voted Resident Evil. Probably my first horror game, and one of the first 3D games I saw. It was a groundbreaking experience.
Early Tomb Raider games were great too. My father (not a gamer) had Tomb Raider (and Resident Evil) on his bussiness PC which I had limited access to, but I only played TR2, 3 and 4 on PS1 and didn't get around to playing the original game.