Too short mostly....
This has the beginning of a good storyline, but the use of little balls with eyes isn't going to get you any points. You seem to have spent a lot of time drawing, but if you want this to be really good, you're going to have to make it more than one minute long.
My specific suggestions are:
Improve on the animation a bit--when the ninja turns around, don't make him look like a flipping coin I mean. Make him look like a round ball. Also, sometimes you're going to have to steer away from motion tweens and do some frame-by-frame animation.
When you're using text instead of sound, make sure you can read what the people are saying. Don't put text over the trees, y'know?
When you feel that you're finished, watch your movie critically. People on Newgrounds are more cruel than you are at your worst when viewing your own movies, but don't take any bad reviews personally. Ask yourself, "Would I vote 5 on this movie?"