I've thought about this. It's addictive, but are there overall goals? Worth the Steam price?
$10 is not too bad actually. It's ore like a mini-game suite than a whole game in itself.
The overall goal is to collect all the belts (starting with the white belt all the way to black belt 3rd degree). At each belt level you must beat 5 mini-games (each one rewarding you with a gem) before you can qualify for the Belt Test.
From an artistic side I think they did an excellent job with the style and quality of it all. The Steamworks edition (PC version) has a lot of Valve-related implementations i.e. Lambda symbol here and there, occasionally the Portal cube etc.