After debuting with a forgettable Double Dragon clone in the arcades, the NES version took a downgrade in graphics but made up for it with gameplay.
Ninja Gaiden on NES is almost like Castlevania but much faster and with ninjas; instead of whip-cracking Europeans. You move like lightening, use ninja stars, sword slashes, and some decent power-ups among your epic quest.
And it's an epic quest indeed. Harder than you could ever imagine too! Once you get to this scene where Ryu Hayabusa reaches the castle; prepare to give up all hope because those stupid eagles, and other hell-spawn will give you a run for your money. Even if you get stuck here; the levels prior to it are still fantastic, and can almost feel like a whole game themselves.