I don't know when highly trained assassins -- known as ninja in feudal Japan -- started becoming such heroic good guys, but this Shinobi fellow has certainly made a long career of it. It's a good thing though, because had he decided to retire after the original Shinobi we would have never had the opportunity to see the greatness that is Shinobi: Return of the Ninja Master.
Shinobi III follows the same gameplay formula as the other 16-bit Shinobi games, Shinobi walking along in a side-scrolling fashion as he dishes out kicks and throwing stars at all the baddies, though he's sporting some new moves in this one that we've never seen before, including the ability to jump up walls or deliver a devastating ninja kick after leaping high above his opponents. Shinobi is also armed with ninja magic that he can use once per stage. Hitting the start button brings up the magic select screen, where you can choose from an energy shield that absorbs attacks, offensive spells that inflict mass damage, or even a suicide spell that instantly kills you (!).
In terms of difficulty, Shinobi III does seem a harder game than either the original Shinobi or sequels like Shadow Dancer. One of the reasons for this difficulty (and a cause of much frustration) is the amount of platform jumping to be found. I personally have fallen to my death more times that I can count in this game.
Graphically, Shinobi III is the most impressive Shinobi game there is on the Genesis. The graphics are colorful and very detailed and some of the bosses look absolutely amazing. The music and sound effects are great too, and there are some nice little touches like Shinobi's ki shout that he sometimes makes when attacking, or when using his ninja magic.
From both technical and gameplay standpoints, Shinobi: Return of the Ninja Master is an outstanding game that, if you can handle its difficulty, will not disappoint.