Shinobi as it should be.
The levels are built to optimize the functionality of the gameplay mechanics. Wall running and jumping is key to advancing, and a wrong move will earn you a big old pile of death. Wall running also plays a critical role in combat in the later levels.
The combat difficulty of the game is very well balanced. You have the sword Akujiki which drains your life unless you feed it the blood of your enemies. Fortunately, attacking multiple enemies will give you more powerful attacks, and lead to greater style points at the end of the level. You can also target an enemy and dash behind them to lay the proverbial smackdown. There is no enemy you can't handle, so long as you suck it up and keep at it. Boss battles show no mercy, but once you reach that point, you won't be sent back to the beginning of the level for dying.
I enjoy the graphics style in this Shinobi. I have seen many criticisms of the level design and display, but I think that the levels serve to advance the player through higher levels of combat encounters. With the sword draining your life, you don't have much time to analyze the texture mapping on the corner of an alley wall. Boohoo. The cutscenes are gorgeous, and the visuals are very smooth over all considering the amount of action going on during each scene.
The soundtrack to Shinobi is fantastic. It refrains from being bland techno, and really helps to keep the fast pace of the game going. The sound effects in the game also really add to the experience.
Another comment on the difficulty. Just try again, loser. Back with NES if you died, you continued and did it better the second time around. Gasp! Improving your skill through practice?! The audacity. Shinobi is definitely a game that will test your true ninja skills, and if you can't handle it, you have dishonored your family and should disembowel yourself.