I enjoyed this movie, but I was disappointed that it wasn't as cool as I was hoping a movie about Ninjas would be. It was basically a big-budget exploitasian flick that had some fun, but ultimately wasn't as cool as I was expecting it would be. Some of the fights in it were good, but a lot of them were horribly shot, using closeup shake-o-vision at its worst and then covering the screen with CG gore to hide the bad choreography. Even GI Joe managed to have decent Ninja fight scenes that were well shot with no ambiguity, so for a movie called "Ninja Assassin" to fail to live up to the fights in a movie that's not even primarily about Ninjas is a little saddening. You could re-create some fights in this movie just by going into a dark room, flapping some black cloth in front of a camera, and squirting a ketchup bottle everywhere while violently shaking the camera.
The pacing in the movie was a bit of a mess, too. I was expecting the movie to be about the main Ninja hunting down his former comrades and having awesome fights with them, but it was mostly just flashbacks of his training while the token Westerners provide exposition for things that usually either aren't important or we can figure out on our own. The middle of the movie was a slow mess, and for a movie that's only 1 hour and 38 minutes long that's surprising. For some reason, the story almost reminded me of Beverly Hills Ninja if it were played straight-- and with less character development.
Don't get me wrong, I liked the movie, and I'll probably buy it on Blu-Ray. However, I think that a lot more could have been done with the concept in the right hands, and sadly, even though this is one of the better Ninja movies I've seen, I can't call it the best. It all around wasn't good enough to overcome my nostalgia for the first Ninja Turtles, the fights were too sloppy to beat out GI Joe, and Azumi is just plain all around better-- and what was very disappointing was that Ninja Assassin was not as fun as any of them.
Like I said, I liked it, but if you want a definitive Ninja movie, you're probably still going to find yourself longing (until I make mine, at least

).