The hardest game I played is "Flashback: The Quest for Identity" for the sega. It's about a man in the future who for some reason is being chased, He just escapes and crah lands in a planet with money, guns, people, robot's, ect. There are puzzle's That are reallly hard. Your main goal is to go back to earth by buying a ticket. The only way to buy the ticket is by doing task that people will pay you for and going to into game show's where you fight for you're life. This game is one of my faverate and I still havent even beaten level 7... There are 100 level's. Flashback is listed in the Guinness World Records as the best-selling French game of all time.
Snapshot-
http://delta.ssakhk.cz/home/zdenek/e.../FlashBack.jpg