This game's nice Target Practice!
Though quite simple, gameplay is pretty addictive and fun!
I also loved how you played around with level creating , having very different challenges each time. The bonus point system was a good idea as well.
As others have said - it's a bit troublesome to guess where the balloons are.
Keep the scrolling option 'cus it definitely adds to gameplay, but adding a minimap like you offered or perhaps just adding colored arrows which pop up at the sides of the screen to show where balloons might be?
A thought - why not add an endless mode were balloons keep popping up? You lose when...too many balloons fly away or something.
Try and playing around with the format - you have a great idea in your hands - but see if there are other ways to present it than simply by levels - having different modes would definitely add gameplay value!
Thanks for the game and hope to see more from you soonsest!