The three original Ninja Gaiden games comprise one of the best trilogy of games on the NES. All three are very similar yet slightly different. They are fast-paced ninja games that feature cutscenes between stages. These games are notorious for their high difficulty and are really fun to play.
Ninja Gaiden III is the most polished game out of the three. The graphics are a little more detailed and nicely animated than in the previous two games. Ninja Gaiden III also has a more 'balanced' feel to it. Ryu moves a little slower and the enemies do not regenerate if you kill them then scroll the screen back. This was a large complaint with the first two Ninja Gaiden games and is responsible for much of their difficulty. In Ninja Gaiden III, when you kill a bird it stays dead.
Ninja Gaiden III is probably the easiest Ninja Gaiden game. With a little practice you can just run through most of the levels. The game wants you to utilize the sub-weapons frequently and doing so makes this game much simpler. Bosses in Ninja Gaiden III are all very easy. They all have very noticable patters and never really pose a threat. Ninja Gaiden III features the Dragon Sword upgrade, which is very powerful. The Japanese famicom version is a little easier than the NES version. The NES version has a limited number of continues and the Famicom version has a password feature.
Ninja Gaiden III is an awesome game. It looks great and it plays great. Ninja Gaiden III is a game that may seem very hard at first, but with some practice it becomes very easy.