I didn't find it fun.
---- I strongly felt that the difficulty gradient was too shallow. As I so often find (with online games), 90% of the time was spent getting to a point where the game became interesting.
-- Interpolating one or 2 steps in the 'defence' mode would have been nice. (i.e. hitTest for 1 or 2 extra points between the previous frames _x/_ymouse and this frame's.) As it is, I often felt I should have picked up some balls.
--- In survival mode, the power-ups meant that sometimes death felt a bit unfair. Not entirely my fault.
++ Lots of modes
+ recognisable/sensible symbols used for power up/downs.
If it was the survival mode and it just got speedier at a faster rate, I would have preferred that a lot.
To be honest, I see no reason to raise the speed in 'steps'. Why not in a gradual shift?
As it is, maybe you could have considered the 'Game & Watch Gallery-style' difficulty curve - the speed raising quickly, then dropping to slightly above its original speed each time the level is increased.
It's basically just a seperation of the 2 elements seen in games such as Gavin Shapiro's 'Squares'. Fair enough, you've presented them in your own way. But I think a little more work was necessary to make this truly fun.