I think a great way to improve the game is to add different functions to the blocks depending on their colour, and maybe add some falling things like powerups/powerdowns so that there is something else to keep track of while the ball is up top, to keep the gameplay from being repetitive. The "2 hits to break" for the cyan blocks towards the end was a great example of a way to spice up the gameplay.

Otherwise, this is a fantastic demo! Keep up the good work!