Cubes fall from the top of the playfield. You can position them using the arrow keys, or rotate the colors and must make matches of 3 or more of the same color. Matches can be horizontal, vertical or diagonal - which is important to remember to complete the levels.
It's just the classic Sega game Columns and all the better for it!
Visually it's lovely, with subtle 3D effects all over the place, from the buttons to the background. The voice overs and music really help bring it alive and as with all games of this genre, it becomes addictive fast.
It reminds me a lot of the original Bejeweled, not in the gameplay, but in the presentation and sound, which is no bad thing. Well worth a play!