Where to begin....
I automatically deduct 1 points if a game fails to give a replay button at the end screen, forcing the player to refresh the screen to start over. I also deduct a point if I find myself dying within the first half second, because I wasn't ready. You usually give people a few seconds for them to acquaint themselves with the controls, no matter how simple those controls they may be. As is, both of these negatives give the impression that you were trying to make a game that would give you as many hits as possible with cheap tactics, with little effort.
As for the rest of the game... not much stands out, other than the magical appearing ninjas in the middle of the screen, and the lack in ability to hit 3 enemies at once, allowing the 3rd enemy to kill you.