Yay and spawn a new ball whenever a primed ball hits the top of the top brick of a stack, don't require the brick to be in the top row.
Never spawn a ball inside bricks.
Add ball spawn animation.
Don't make brick collidable until the spawn animation is partially complete.
Display a score banner for sufficiently impressive scores.
Sometimes display a silly saying instead of a score banner.
Refactor and improve banners.
Remember to reset banners.
Improve banners some more. Add banners for lost balls.
Add 'it's all gone wrong'
Add 'spiffing!'