Fun little concept, a few things would be fun to see if possible
- Using a filled bar for a "special" attack of some kind like temporary walls that stop the ball or auto play for a few seconds, something to reward the player for not needing to block
- Add the ability to charge an attack, more power, more risk, more reward
- A local 2-player mode for either a pong style battle or highest points
- Characters to play as with unique attacks
- Color customization
None of these are requirements, just suggestions for the future.