Gamasutra has a list of what they believe to be 20 of the most difficult games ever created. As you may have guessed, most of these games were released in the 8-bit era. Many popular game series make the list, including The Legend of Zelda and Monkey Ball.
Difficulty in video and computer game development has been on the outs for some time. If a player possibly cannot complete Action Adventure Game X, so the thinking goes, the designer has failed. Most MMORPGs feel like they can be played on autopilot; in fact many can, a fact dear to some players' hearts. When Ninja Gaiden came out and turned out to be a stiff challenge some players were up in arms. That ever-so-quotable Tomonobu Itagaki said that hearing player cries made him want to make the game even harder.
Ahem. Setting aside what we might think of his statement, certainly, difficulty in a video game must be handled carefully. Nothing attracts the ire of those fickle game bloggers quite like them getting their asses handed to them by a game. And it is possible to make a game arbitrarily difficult without too much effort. Increase monster attack strength, decrease player health, remove resources and adding more foes, there are just the most obvious ways a game can be made harder, and it doesn't take any great skill to add them.