It just feels like a more refined game than Ninja Spirit.
Shinobi III totally *is* a more refined game than Ninja Spirit. More complex too. It's got tons of lovely control mechanics that are fun to use. The double jump + shuriken shower, the air kick, the double tap run, the ninjitsu magic. Not to mention carefully placed enemies and tricky level design. Ninja Spirit has none of those things... because it doesn't need them. Ninja Spirit just isn't that kind of game. Ninja Spirit is all about wave after wave of enemy ninjas swarming you, picking the right weapon for the right part of the game, timing your jumps and movements just right, and clearing a path through the madness so you can get a crack at the boss. Ninja Spirit is, for all intents and purposes, a run-n-gun sidescroller masquerading as a ninja themed platformer. And it pulls it off perfectly. Shinobi 3 is the culmination of an entire series. Sega had 3 previous games to experiment, hone and perfect their formula. Ninja Spirit, however, is one of a kind. I think the whole debate between Shinobi 3 and Ninja Spirit is really a debate over which genre of game you like better... action platformer or run-n-gun sidescroller. For me, the answer is easy... I'll take stuff like Contra, Ninja Spirit, and Gunstar Heroes over Shinobi any day of the week. Apparently my son will too lol