I really liked the idea! It is unusual to want to have a fair game and to sometimes root for the opposing side. I noticed that if you clicked play after a round was over the game bugged and you had to restart.
Nice with a leaderboard, I came third my first time. Tried it again and after a couple of tries I got the second place. Man it got addicting quickly, my favourite game so far :D
I found some other bugs:
I think that the pieces that survived the previous round got to fire quicker than the pieces you placed.
Usually when the game ended the pieces shot a ball straight up.
Nice work!