This is what ninjas are all about!
This was really funny!! So much good i only want to talk about the bad:
The Ninja... he looked a bit weird.
The blood and shurikens on the ground stayed the same place when you advanced in level (maybe that was on purpose?)
The fact that it was arcade style. It could just have been a feature, so you also added a campaign, training stage etc.
That's about it, if you could fix/add this, i would give you a 10 :)