exponentially frustrating
collision detection is a bit flaky (especially for the non-glowing green ball) and spoiled a couple of my "close passes"...
but it is really getting hard exponentially fast... every hit takes away 3 points (right?), with every level there is one more green ball to avoid (right?), yet to advance to the next level you must get more and more points...
Because each green ball hit is worth 3x the blue ball, the time to increase your score by 1 increases much faster than the level. Yet, you must get more points to advance to the next level... So, each level is much much more harder than all that precede it.
... or it's just me that sucks (I got to level 6).