heh, I bet EVERYONE here remembers Super Ghouls and Ghosts. hands down the most difficult game of all time (besides Bart's Nightmare, but thats due to purely horrid gameplay and controls).
Bart's Nightmare was more Gamer's Nightmare than anything. It was just a collection of the most crappy minigames (covered up with Simpsons graphics, although most Simpsons games were like that; they never actually centered around the actual show), which weren't necessarily hard, but just downright no fun. Plus, the system of walking around on the streets to find a random piece of paper floating by made for such a slow start-up that players were likely to have switched their systems off before ever actually having played a game.