Game: Doom
What Makes It Bad: Annihilating the player in any way possible.
What Makes It Cool: A missile-launching skyscraper with goat legs. 'Nuff said.

Back in the day before consoles systems started to rule the world, PC gamers had Doom and a memorable ending boss, the Cyberdemon. id Software delivered terror in droves with this unknown enemy. Unknown to the Doom player, he wasn't even mentioned in the manual for the original PC version. It allowed there to be more of a surprise to the player, who was brave enough to reached the hellish beast at the end. Being an unfeeling half-demon, half-machine, he deserves a place on the list.