I couldn't go past the third level, hahahaha. Anyway, as most people already said, it is very difficult. I also think you could introduce more mechanics to don't have the game become old too quickly. You could also tweak the hitboxes more in favor of the player as well, it gets really hard to click the circle when it's too small, and the minimal touch of the other balls on the center one kills you.
Other than that, I like the minimalistic graphics, really shows that a game can look good without much work drawing.