I think puzzle games and the shooting games tend to be difficult due to the sniper element in the shooting and the mystery part in the puzzle games. But those are worth playing as those games tend to be good for the mind exercise.
I remember about five or six years ago, when I first discovered The Worlds Hardest Game. Boy, that was certainly a struggle.
And of course, who can forget Dark Souls, or Dark Souls II, or Dark Souls III? While I never played any of the Dark Souls games, they were certainly infamous among the gaming community.
xenonVirus. It's kind of hard to define the world's hardest game, because everything is subjective depending on who you ask.
Skyrim but I first played that when I was younger so it may have just been because of my age. It also didn't help that I didn't like the game that much and certain aspects annoyed me so I probably didn't pay enough attention to be good at the game.