Dude, your movie about ninjas bored an ADHD into sweeping the floor.
Ninja Assassin, during the childhood flashbacks, I swept my room.
Yes, I'm ADHD, but honestly, I felt like I've watched it before because I could predict the plot so well. While simple may be solid, it doesn't really work for this movie.
Or maybe it does. While the plot may not be in any way considered brilliant, it does have fairly decent acting and awesome effects.
By which I mean eye candy by Korean star Rain, and huge amounts of fake blood.
So, if you can fast forward, ignore or sit through the flashbacks, this movie is great for the blood spilling! Enjoy!