There were many games that came out on the NES that many would consider "NES Hard". A term that came about due to the fact that many of the games of the 1980s were that stupidly difficult, they required split second timing and pixel perfect jumping.
Ninja Gaiden was released by Tecmo in 1989. The game is a redesigned version of the arcade game. However the difficulty ramped way up. If there ever was a single game that would have defined the "Nintendo Hard" moniker, this would be it.
Ninja Gaiden plays very similar to Castlevania, but is more fast paced. It requires expert timing, pixel precision platforming and more. This was a game that was designed to eat the 8-bit gaming newbies alive.