I love this game, and was excited to find a decent iPod app with it. A few suggestions -
Would be great to be able to earn bombs which could clear out some balls on the board. I've played a version where you slowly earn bombs, and can use them whenever, although the longer you wait to use, the more balls get exploded from the board.
In this other version I've played, you're encouraged to make longer lines (points are more exponential). Its also beneficial to explode lines one after the other (earns more points and new balls don't appear until moving a ball doens't make a line). In your version, there seems to be no reason to wait to explode a line or make ones that are longer.
Even so, this is one of my go-to games. I haven't tried harder levels because I can't seem to get beyond level 12 on easy, no matter how many times I've played.