"Addictive" is the word for this one -- make sure you've got plenty of time to play before you start!
The object of the game (which is a little like "Tetris") is to line up sets of five or more six-sided crystals of the same color before the new crystals fill the screen.
Lots of different skill levels are available, from easy to super-hard. And don't forget about options like music, sounds and animation.
The game is easy to learn, easy to use and very hard to put down!