Having never seen any of the series but being familiar with many Samurai movies from the same era, I found Shinobi No Mono to be very similar in form to the traditional Chambara formula... albeit a bit more action packed. However as with most early Chambara, the film features a complicated plot, well-developed characters, and striking imagery courtesy of cinematographer Yasukazu Takemura.
The big draw of Shinobi No Mono is the martial arts and the film delivers in that aspect. Being one of the first Ninja movies, the film is packed with fight scenes and cool ninja tricks. Shuriken's are thrown, gunpowder ignited, and grappling hooks are used in ways they weren't intended. The film is particularly interesting because it helped create quite a few modern day movie cliché's.
For instance, there is a scene where Guemon tries to dispatch a target by sneaking into his attic, drilling a hole in the roof, dropping a string down, and sending poison down the line in an attempt to land it in the sleeping target's mouth. This scene was later imitated in numerous films including George Armitage's 1997 black comedy, "Grosse Point Blank." Other than that, many of the newer breed of ninja movies feature a lot of the same "secret ninja moves" that were made known in Shinobi No Moni.
My only complaint is that sometimes the plot feels needlessly complicated. If your familiar with other films from this era you shouldn't have a problem following the film. But if you're not, you'll probably have to pay close attention because the plot intricacies come fast as the betrayals, set up's, and alliances pile up.
Bottom Line- Interesting and complicated seminal ninja film that's as fun as it is action-packed.