"Shinobi" is Japan's attempt to make a big martial arts fantasy epic, obviously inspired by the success of "Crouching Tiger, Hidden Dragon" and the revived interest overseas in Chinese wuxia flicks. The problem is, martial arts fantasy isn't really Japan's forte. Japanese period films tend to focus more on the duty/passion conflict inherent in the samurai, whose sword-skills are precise rather than flashy. A single-cut kill is the apex of the art of the samurai, not flying around on trees and flinging millions of little knives all at once.
As source material, the 1959 novel "The Koga Ninja Scrolls", previously adapted as the anime series "Basilisk", was a good base, using the traditional conflict between the Iga and Koga ninja villages with a Romeo/Juliet love story thrown in for good measure. (The director is sure to hammer this point home, even stating several times that the two are "star-crossed lovers"). Director Ten Shimoyama was also a good choice, having experience in the Chinese action film industry, and was able to supply some of the dramatic action that is a hallmark of that genre. The lead actress Yukie Nakama brought some star power, being probably the most popular actress in Japan today. They were even good enough to skirt around her inability to fight, as Yukie has all the martial arts ability of a broom stick. But she does have an awfully pretty face, which was used to full effect.
All in all, "Shinobi" is a good flick, better than I had expected. There is not really the experience there, either on the part of the actors or the director, to produce a really moving martial arts fantasy, but everyone worked with what they had, keeping the action low-key and making the emotions of the characters the focus. Because the basis of the story is the Romeo/Juliet conflict, nobody is really expecting a happy ending, but even with that in mind the character's deaths have impact, and even then not everything turns out exactly as expected. Some of the choices were odd, and I am not really sure what is the point of including legendary warriors Hattori Hanzo and Jubei Yagyu in the plot without sending them into battle, and they serve as little more than recognizable set decoration.