You have no idea how frustrated i was before i found out how to shoot XD. Make your game more intuitive or include an in-game tutorial! I thought you had to block with your circle. Also, the art looks great, but the sprites don't all fit together in one artstyle. But besides that, nice idea and absolute fantastic thumbnail! Could be the thumbnail of an fully released game! I just think the game lacks some polish like animation of score, general animation, more consistent artstyle etc.
Anyways, i hope that my feedback helped you a bit, and it would be nice if you could check out my submission too. Thanks! :)