A short, and yet very fun game... I'd like to see something like this on mobile apps... especially if you could compete for high score amongst your friends.
It wouldn't HURT to have levels and challenges, but it really doesn't need it.
Artwork... the balloons look like balloons, and the arrows look like arrows... it more than suffices... but before the start of the game after you hit start, there doesn't seem to be much of a delay... maybe a few seconds of, maybe, a clown with an airtank climbing over the wall to the back side or something of that nature to denote more of a "get ready" message would do it good... kinda like the dog in Duck Hunt.
I can't say anything about the sound as my soundcard isn't working...
Good job on a simple and fun game.