This feels not-quite-fully-developed... close but not there yet.
Graphics fine, gameplay smooth... but something is missing. Simple things, like opting for a "first to 10" or "first to 20" or "endless play" game. This would add much more tension to the game - there's very little tension if the scores go on endlessly.
Perhaps a limit on the number of times a player can hit the ball before getting it over the net (it's boring watching the computer play keepy-uppy with it).
Don't let the ball come to rest on the net. Or give it a timer, so that if it gets stuck, it blows up, to the penalty of whichever player failed to get it over, or perhaps hit it last (in the case of a player bouncing it straight off their opponent's wall).
Maybe give the computer easy, medium and hard modes - that shouldn't be too hard to do, simply restricting his speed ought to be enough.
This is very close to being an excellent little game. As it is it's a fun timewaster but it seems a bit of a waste, for all the effort that went into the gameplay and graphics, not to have taken the game design a bit further.