36. Doom (PC)
No, not the 'xxx is doomed' game that we often play on these forums, but the classic FPS. Pre-dated only by Wolfenstein 3D, Doom was one of the very first games of its kind, and arguably, it was the one that popularised the genre. I think I was about 10 when I first played this (parenting win!), but I managed to avoid warping my fragile little mind. Mostly....
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