One of the Master Systems best titles and one of the better Shinobi ports
The original is slower paced than the other games, with usually only 1-3 enemies on screen at once, and these are dealt with by using a little thought rather than hacking mindlessly.
Unlike later games this involves saving children, which give bonuses that come in useful, especially for the boss battles which are cheap. It also has a mini game between levels that award magic.
It's not a very hard game when you figure it out, and can be run through in about half an hour. The main issue are the boss battles, particularly the last two which go from requiring a modicum of skill to battling unresponsive controls.
For my money the Game Gear Shinobi games were alot better, The G.G. Shinobi II: The Silent Fury being better in every regard and and a visual stunner at the time which showed what the Game Gear hardware could do.
Still a good game, worth a punt if your bored.