Indeed the game loop is quite clever, simple and addictive like you said, you can easily spend a lot of time with this, but I do miss a couple of things that I think woul make this even more addictive an add more depth ...
since it is a small interface I keep thinking this was meant for mobile and in the mobile this could make good use of accelerometer in clever ways (well, you might have already thought about it cause it was the first thing that crossed my mind on my first minute of gameplay) ... like, I want to have more ways to control the movement of the ball, so I feel there is depth to be explored and expertise to be earned ... like games that are easy to get started an feel the addictiveness, but can also offer some depth for those that want to be the best at it. I do imagine people moving their mobiles like crazy to get high scores though lol.
Great concept!