I would say this is most certainly one of the greatest puzzle games out there, and like all the great puzzle games it has a simple premise with fantastic gameplay. You control a beach-ball, and you have to collect keys to unlock the exit. The catch is you have to negotiate your way through bizarre 3D structures avoiding traps and other assortment of hazards. The music is pleasant, the stage design and art design are great, and with 150 levels (plus 20 bonus stages when you complete the main game) this will surely keep you occupied for a while. Old copies for the PSone might be hard to track down but the game is available on the Playstation Store, although I'm not sure if it is available in the US and Japan regions on the PS Store (the game was released as 'Roll Away' in the US, 'Kula Quest' in Japan) and I believe this game has also been released on Android.