Fun game all round. It's a little bit too easy to overpower your plane early on, but that does add to the satisfaction of decimating enemies.
I did encounter a few bugs in the game. I wasn't able to get sound to work on Chrome, but it worked fine on Firefox. And on level 11, I had a strange glitch that started out when the game began to lag with so many sprites on the screen. The sprite for my plane turned into a green looking explosion and the coin counter went out of control. Even when lag stopped and the game returned to normal, the coin counter kept on racing. But it returned to normal next level (though I now had over 160,000 coins).
All in all, I'm a fan. :-)