Well done!
I think that your game is fun to play and I believe the core mechanic is fun and unique. I really like the fact that there are a variety of enemies and I also love the trail and explosion effects :D
One thing I think could be added would be music and I also find that the square ball/projectile often didn't bounce back as I expected it to, this could have to do with the fact that its a square and not a circle, I found this unpredictability a bit frustrating as it almost felt a bit unfair.