7. Every Modern Ninja Gaiden
http://youtu.be/aO7NILnmURU The modern Ninja Gaiden franchise is so horrendously difficult that I personally can't face it any more, despite the fact that it's actually a fairly awesome series. Ninja Gaiden doesn't simply deliver a challenge, it delivers pure punishment, for a crime it doesn't actually care whether you committed or not, in the form of infuriating hordes of enemies and ridiculously overpowered bosses that murder the protagonist as easily as they'd murder you yourself. Completing a Ninja Gaiden title takes a certain kind of gamer; one who's willing to try again, and again, and again, and again, until finally he or she gets lucky once and finally clears the tutorial. Next task is level one! See you in two weeks!