For the most part, I would say that the people who have posted in this thread have had it fairly easy if the majority of you can only complain about games which came out in the past decade, and to those of you who cite legitimately terrible games as the worst game they've experienced, I will concede that Custer's Revenge, ET, and Superman 64 are terrible games, but having played these games and many others, the biggest exercise in complete and utter gaming frustration for me personally was the atrocious "Jim Power: Lost Dimension in 3D" for the SNES, if you don't want to take my word for it, download a copy of it for yourself and see if you can even make it past the first level.
Enjoy.