It's easy to tear a movie like Ninja Assassin apart.
It's completely mindless action, the plot is pretty lousy, and there's no reason to care about any of the characters.
That said, I actually had fun watching this movie. This is one of those movies where when you break down all of the elements, you can't really find anything of real quality. Yet at the same time I was pleasantly surprised by this film. I thought it would be completely unwatchable due to the acting and the over the top violence, but as long as you don't try to take it seriously, you can have a good time. Don't get me wrong, it is extremely (and at times needlessly) violent. Limbs fly, heads roll, and blood sprays all over the place, but this is probably the first movie I've seen where that kind of violence hasn't been an annoyance. This is probably largely due to the fact that I wasn't trying to connect with the film on any sort of higher level. There's a right and a wrong way to do mindless entertainment. I think Ninja Assassin got most of it right, and while it may not be a "good" film, it can certainly keep you entertained (if you can stomach seeing all that blood).