Ninja Cop (also known as “Ninja Five-O“) on the Game Boy Advance is a brilliant side-scrolling action game. Sort of like a cross between Shinobi and Bionic Commando.
The main character is agile and deadly, and gets to swing all over the place, and you do feel like an actual ninja (and a cop) when you master the controls and start making progress.
A classic action combat game from Hudson Soft and Konami!
Note: although Ninja Cop was developed by a Japanese company, it was never released in Japan. For some reason. Which is bizarre!
More: Ninja Cop on Wikipedia