It will both entertain and frustrate you, but through it all, Ninja Gaiden NES is a bonafide classic.
The game is loosely based on the arcade game of the same name (which I played a few times), but this is by no means a direct port. The story revolves around the solitary superninja Ryu Hayabusa, a beautiful CIA agent, two demon statues and a conspiracy that threatens to envelop the world in darkness. The game is structured very much like any traditional 8-bit action game. You'll scale walls, defeat enemies with a ridiculous respawn rate, take down some creepy bosses and do what ninjas do. What makes this game different from all the rest are the memorable cinema scenes. There is a great emphasis on story, and it clearly shows. It's well-written and the characters have a distinctive personality in spite of their shortcomings.
But as fun as the game can be, it is also one of the most challenging Nintendo games to date. As I said earlier, you will have to contend with enemies that will constantly reappear. You will also be forced to deal with getting helplessly knocked backwards every time you get hurt. Expect to stupidly fall into more than your fair share of pits from mediocre enemies. The Ninja Gaiden series are notorious for its high level of difficulty, and this game is no different. Any degree of satisfaction felt when the game is beaten is invariably earned. Any broken controllers, shattered plasma screens and profanity incurred is certainly understandable.
It's not my intent to deter you from playing this game--if anything, the difficulty will please anybody looking for a good challenge, and Ninja Gaiden delivers on that promise in every way. If you think you're ready for a game like this, by all means--download it from the Shop Channel and have at it. Just know what you're getting yourself into!