What's the hardest game you've played?

Glover for the Nintendo 64.

I have to this day not beat it lol.

Glover isn't hard really...
Its just REALLY REALLY glitchy and the controls suck.
Once you get good at moving its easy to win.
Which takes FOREVER

Have not played it, but I know Ghosts and Goblins has a reputation for being insanely hard.
First you beat it, then you go to level 5 again, then you beat the whole thing again, with three lives and two hits to lose a life. Impossible to beat without H4x0rz.