It depends of if you mean "Intenetionally hard and wants to wrestle you to the floor and make you his bitch" or "So hard because the controls are utter crap, even though it's a good game"
Hardest games I can remember playing are Ikaruga, Ghost and Goblins, and this old NES Castlevania.
Ones hard because of shit controls are Castlevania 64 and Hex.
Both of them are pretty old platformers.
My computer's breaking down, so nope.
"Most people think they're thinking, when in fact, they're just rearranging their prejudices."- William James