Ninja Cop has a quite an interesting history, and was initially developed by Kyugo, for Konami, way back in 1989 for JAMMA compatible arcades, whereupon it was fully forgotten amid the slew of side-scrolling action games of the time.
Similar in appearance, though not in delivery, to such gems as Shinobi and Bionic Commando, Ninja Cop, known as Ninja Five-O in the US, is a side-scrolling action game, the likes of which havent been in favour for a decade.
Possessing one of the best game titles since the late eighties, the game, which incidentally is made by Bomberman specialists HudsonSoft, is set in Hawaii, where some bad guys, possibly drug-dealers or terrorists or something, have done something, or kidnapped someone or are threatening the stability of the world somehow. Or something. None of that really matters, as the outcome is the same: You walk along, from right to left, and as enemies come into range, you kill them, whereupon they fall to floor and vanish.
And that really is about it. Ninja Cop represents that golden age of gaming, when things were simple and people were happy with gameplay that offered little more than steady progression through themed levels.
There are some adherences to the modern (and arguably more cynical) world of videogames, such as gameplay extension via the magic of unlockable weapons and other bonuses, operated by a points system, but thats really by the by.
If you pine for the good old days, or are interested to see just how boring gaming used to be a decade ago, you could do much worse than play Ninja Cop.