The gameplay is nice but I feel like the boomerang guy needs some tuning. It almost seemed like I countered myself since my boomerang was slower than anything else, including myself. The ninja was sick tho. ;)
The audio and graphics are also very good. Personally, I would reduce the screen shake a little, at least when you play the ninja.
Overall, I had a lot of fun playing the game (especially the ninja) and I think you did a really good job.